Premium
Some properties of Ca(2+)‐induced Ca2+ release mechanism in single visceral smooth muscle cell of the guinea‐pig.
Author(s) -
Zholos A V,
Baidan L V,
Shuba M F
Publication year - 1992
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1992.sp019362
Subject(s) - chemistry , biophysics , nifedipine , membrane potential , calcium , voltage dependent calcium channel , patch clamp , guinea pig , voltage clamp , endocrinology , receptor , biochemistry , biology , organic chemistry
1. Late transient outward Ca(2+)‐dependent K+ current (ILTO) correlated with Ca(2+)‐induced Ca2+ release mechanism was studied in relation to the calcium inward current (ICa) in single isolated smooth muscle cells of the guinea‐pig ileum using the whole‐cell patch‐clamp technique. 2. The voltage dependencies of peak ICa and ILTO were both bell shaped. However, the I‐V curve of the outward current was shifted toward more positive potentials by about 60 mV in comparison to that for ICa. 3. Reduction in the external Ca2+ concentration resulted in a decrease of peak amplitude of both ICa and ILTO. However, caffeine‐induced outward current was also decreased abruptly suggesting a rapid loss of stored Ca2+ upon lowering the external Ca2+ concentration. 4. Investigation of the relation of ILTO to partially inactivated ICa showed that inactivation of ICa by approximately 65, 80 or 84% of control (produced by prepulse to ‐20 mV for 2 s, shifting the holding potential to ‐20 mV for 30 s or by the ramp voltage command from ‐50 to +10 mV, respectively) was without detectable effect on the ILTO generation. 5. Bath application of the Ca2+ antagonist nifedipine (300 nM) inhibited ICa by 81% without affecting ILTO peak amplitude (92.0 +/‐ 5.6% of control in six cells). The mean concentration‐response curve for ICa inhibition was sigmoidal with the apparent dissociation constant of 86.9 nM, whereas that for the ILTO had a characteristic sharp transition indicating a definite threshold of Ca2+ influx for ILTO generation. 6. Application of Ca(2+)‐free external solution during 500 ms of the time when ICa peaked inhibited the current by about 76% whereas the ILTO during such an intervention remained virtually unchanged. 7. In double‐pulse experiments, with conditioning and test pulses to +10 mV from ‐50 mV and an interpulse interval of 600 ms, most of the cells (about 80%) showed larger outward current at the test pulse suggesting continued Ca2+ release triggered by Ca2+ influx during a short (50‐200 ms) depolarizing prepulse. The outward current could also be evoked at large positive potentials (presumably near the calcium equilibrium potential) where it did not occur normally by a prepulse to +10 mV for 50 ms. The charge transferred by Ca2+ current necessary to activate Ca2+ release in most of the cells was estimated to be from 6 to 20 pC. 8. The data are interpreted to suggest that the Ca(2+)‐induced Ca2+ release mechanism operates in single ileal cells in a regenerative manner.(ABSTRACT TRUNCATED AT 400 WORDS)