Abstract
T‐type Ca
2+
currents have been detected in cells from the external muscular layers of gastrointestinal smooth muscles and appear to contribute to the generation of pacemaker potentials in ...interstitial cells of Cajal from those tissues. However, the Ca
2+
channel α subunit responsible for these currents has not been determined. We established that the α subunit of the α
1H
Ca
2+
channel is expressed in single myocytes and interstitial cells of Cajal using reverse transcription and polymerase chain reaction from whole tissue, laser capture microdissected tissue and single cells isolated from the mouse jejunum. Whole‐cell voltage clamp recordings demonstrated that a nifedipine and Cd
2+
resistant, mibefradil‐sensitive current is present in myocytes dissociated from the jejunum. Electrical recordings from the circular muscle layer demonstrated that mibefradil reduced the frequency and initial rate of rise of the electrical slow wave. Gene targeted knockout of both alleles of the
cacna1h
gene, which encodes the α
1H
Ca
2+
channel subunit, resulted in embryonic lethality because of death of the homozygous knockouts prior to E13.5 days
in utero
. We conclude that a channel with the pharmacological and molecular characteristics of the α
1H
Ca
2+
channel subunit is expressed in interstitial cells of Cajal and myocytes from the mouse jejunum, and that ionic conductances through the α
1H
Ca
2+
channel contribute to the upstroke of the pacemaker potential. Furthermore, the survival of mice that do not express the α
1H
Ca
2+
channel protein is dependent on the genetic background and targeting approach used to generate the knockout mice.
Excitable cells express a variety of ion channels that allow rapid exchange of ions with the extracellular space. Opening of Na super(+) channels in excitable cells results in influx of Na super(+) ...and cellular depolarization. The function of Na sub(v)1.5, an Na super(+) channel expressed in the heart, brain, and gastrointestinal tract, is altered by interacting proteins. The pore-forming alpha -subunit of this channel is encoded by SCN5A. Genetic perturbations in SCN5A cause type 3 long QT syndrome and type 1 Brugada syndrome, two distinct heritable arrhythmia syndromes. Mutations in SCN5A are also associated with increased prevalence of gastrointestinal symptoms, suggesting that the Na super(+) channel plays a role in normal gastrointestinal physiology and that alterations in its function may cause disease. We collected blood from patients with intestinal pseudo-obstruction (a disease associated with abnormal motility in the gut) and screened for mutations in SCN5A and ion channel-interacting proteins. A 42-year-old male patient was found to have a mutation in the gene TCAP, encoding for the small protein telethonin. Telethonin was found to be expressed in the human gastrointestinal smooth muscle, co-localized with Na sub(v)1.5, and co-immunoprecipitated with sodium channels. Expression of mutated telethonin, when co-expressed with SCN5A in HEK 293 cells, altered steady state activation kinetics of SCN5A, resulting in a doubling of the window current. These results suggest a new role for telethonin, namely that telethonin is a sodium channel-interacting protein. Also, mutations in telethonin can alter Na sub(v)1.5 kinetics and may play a role in intestinal pseudo-obstruction.
We hypothesised that bradykinesia may be partly due to the failure of the corticomuscular system to engage in high frequency oscillatory activity in Parkinson's disease (PD). In healthy subjects such ...oscillations are evident in coherence between active muscles at 15--30 Hz. We therefore investigated the effects of therapeutic stimulation of the basal ganglia on this coherence and related it to changes in bradykinesia in the contralateral arm. Increases in coherence at 15--30 Hz and improvements in bradykinesia upon stimulation were correlated (r = 0.564, p < 0.001). This suggests that the basal ganglia modulate oscillatory activity in the corticomuscular system and that impairment of the motor system's ability to engage in synchronised oscillations at high frequency may contribute to bradykinesia in PD.
Critically ill patients are at increased risk of acquiring nosocomial infections. A thorough clinical evaluation and the selection of appropriate diagnostic techniques are important elements in the ...evaluation of these patients. Nonetheless, this selection process can be difficult because of the wide spectrum of disease that is seen in the ICU and the lack of standardized studies that have evaluated the different diagnostic methods that are available. Many different antimicrobials are available for the treatment of ICU-acquired infections. Most antimicrobial regimens have not been evaluated in large-scale, prospective, randomized trials. Until this information is available, the clinician must make an effort to be familiar with the different clinical and epidemiologic variables that can be used to stratify patients at the moment of selecting antimicrobial therapy. The information provided in this article, used in association with good clinical judgment, will help the critical care physician provide optimal initial management of the infected patient in the ICU.
T-type Ca(2+) currents have been detected in cells from the external muscular layers of gastrointestinal smooth muscles and appear to contribute to the generation of pacemaker potentials in ...interstitial cells of Cajal from those tissues. However, the Ca(2+) channel alpha subunit responsible for these currents has not been determined. We established that the alpha subunit of the alpha(1H) Ca(2+) channel is expressed in single myocytes and interstitial cells of Cajal using reverse transcription and polymerase chain reaction from whole tissue, laser capture microdissected tissue and single cells isolated from the mouse jejunum. Whole-cell voltage clamp recordings demonstrated that a nifedipine and Cd(2+) resistant, mibefradil-sensitive current is present in myocytes dissociated from the jejunum. Electrical recordings from the circular muscle layer demonstrated that mibefradil reduced the frequency and initial rate of rise of the electrical slow wave. Gene targeted knockout of both alleles of the cacna1h gene, which encodes the alpha(1H) Ca(2+) channel subunit, resulted in embryonic lethality because of death of the homozygous knockouts prior to E13.5 days in utero. We conclude that a channel with the pharmacological and molecular characteristics of the alpha(1H) Ca(2+) channel subunit is expressed in interstitial cells of Cajal and myocytes from the mouse jejunum, and that ionic conductances through the alpha(1H) Ca(2+) channel contribute to the upstroke of the pacemaker potential. Furthermore, the survival of mice that do not express the alpha(1H) Ca(2+) channel protein is dependent on the genetic background and targeting approach used to generate the knockout mice.
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