HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Wade, G R Articles by Sims, S M Search for Related Content PubMed PubMed Citation Articles by Wade, G R Articles by Sims, S M

Department of Physiology, University of Western Ontario, London, Canada.

1. Cholinergic regulation of L-type Ca2+ channels was investigated in freshly dissociated guinea-pig gastric and tracheal smooth muscle cells. Acetylcholine (ACh, 50 microM) decreased Ca2+ channel current (ICa) by 37 +/- 3% (mean +/- S.E.M., 46 cells). 2. ACh reduced ICa at all voltages, with no shift in the current-voltage relationship. Effects of ACh were rapid (within 5 s) and repeatable, with multiple applications reproducibly inhibiting ICa in the continued presence of extracellular Ca2+ and in the presence of protein kinase C inhibitors. 3. The involvement of Ca2+ stores in this inhibition was investigated using Ca(2+)-free solution or cyclopiazonic acid (CPA) to deplete the stores. ACh initially inhibited ICa in the Ca(2+)-free solution (Na+ as charge carrier, 53 +/- 4% decrease, 18 cells) with subsequent responses significantly attenuated (n = 9). CPA (1 microM) reduced, then abolished, the effects of ACh on ICa (n = 5). 4. When studied in cell-attached patches (Ba2+ as charge carrier), ACh reduced Ca2+ channel open probability in twenty-two of thirty-six cells, consistent with the involvement of a diffusible cytosolic messenger. 5. ACh also inhibited ICa in tracheal muscle cells (reduction of 38 +/- 6% in 1 mM Ca2+, 4 cells; 77 +/- 3% in Ca(2+)-free solution, 7 cells). Furthermore, in cells where ACh elicited oscillating Ca(2+)-activated Cl- current, oscillatory inhibition of ICa was also observed (3 cells). 6. In summary, ACh causes rapid and reversible inhibition of ICa in gastric and tracheal muscles. Ca2+ stores were required to initiate this effect, with the rapid onset and oscillatory inhibition consistent with Ca2+ inhibition of the channel. Suppression of ICa would reduce Ca2+ entry during cholinergic excitation.