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cGMP inhibits the activity of single calcium channels in embryonic chick heart cells
1Department of Physiology and Biophysics, University of Cincinnati, College of Medicine, Ohio 45267-0576.
Abstract:
Effects of cGMP on the slow (L-type) Ca2+ channels of cultured chick embryonic cardiomyocytes were investigated by a cell-attached patch-clamp method. Superfusion of the single cells with 8-bromo-cGMP, a membrane-permeable derivative of cGMP, inhibited the single-channel activity. The cyclic nucleotide decreased, in a concentration-dependent manner, the ensemble averaged currents obtained from multichannel patches. 8-Bromo-cGMP (1 mM) completely abolished the currents (n = 8), whereas 0.1 mM only slightly decreased the currents (n = 4). The influence of cGMP on the characteristics of the single Ca2+ channels was examined using 0.3 mM 8-bromo-cGMP. Unit amplitude and slope conductance of the Ca2+ channel was not changed (25 pS in control versus 24 pS in the presence of cGMP). Analysis of single-channel kinetics showed that cGMP prolonged the slow time constant for the closed-time histogram (from 6.7 to 15.4 msec); the other time constants (for the open-time and closed-time histograms) were not affected. cGMP-induced inhibition of the Ca2+ channels may be mediated by cGMP-dependent protein kinase, because 8-bromo-cGMP is a potent activator of this protein kinase and does not stimulate cAMP hydrolysis. The present results suggest that cGMP opposes the effects of cAMP on the L-type Ca2+ channels in myocardial cells.
Insights
Cyclic guanosine monophosphate (cGMP) inhibits slow, L-type calcium channels in chick heart cells. This finding suggests cGMP opposes cyclic adenosine monophosphate
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Ion Channel Function
Background:
- L-type calcium channels are crucial for cardiomyocyte excitation-contraction coupling.
- Cyclic nucleotides like cAMP and cGMP modulate cardiac function.
- The specific role of cGMP in regulating L-type calcium channels in cardiomyocytes requires further elucidation.
Purpose of the Study:
- To investigate the effects of cyclic guanosine monophosphate (cGMP) on slow (L-type) calcium channels in cultured chick embryonic cardiomyocytes.
- To determine the mechanism by which cGMP influences L-type calcium channel activity.
Main Methods:
- Cell-attached patch-clamp recordings were used to assess single-channel activity.
- Cultured chick embryonic cardiomyocytes were superfused with 8-bromo-cGMP, a membrane-permeable cGMP analog.
- Ensemble averaged currents and single-channel kinetics were analyzed.
Main Results:
- Superfusion with 8-bromo-cGMP inhibited L-type calcium channel activity in a concentration-dependent manner.
- cGMP did not alter the unit amplitude or slope conductance of the calcium channels.
- cGMP significantly prolonged the slow time constant of the closed-time histogram, indicating altered channel gating kinetics.
Conclusions:
- cGMP inhibits L-type calcium channels in cardiomyocytes, primarily by affecting channel gating.
- The inhibitory effect of cGMP may be mediated by cGMP-dependent protein kinase.
- cGMP appears to exert opposing effects to cAMP on L-type calcium channels in myocardial cells.