Effect of Ca2+ channel blockers on K+ contractures in twitch fibres of the frog (Rana pipiens).
1. The effects of Ca2+ channel blockers (nifedipine, nitrendipine and diltiazem) were tested on K+ contractures in single muscle fibres of the frog, Rana pipiens. 2. Nifedipine (1 microM) reduced the area under K+ contractures to 24 +/- 9% (4) (100 mM-K+) and 34 +/- 24% (4) (190 mM-K+). Nitrendipine (0.1 microM) reduced the area to 30 +/- 10% (4) (120 mM-K+). The blockade of the contractures was reversible. 3. Diltiazem (1 microM) shortened the first 190 mM-K+ contracture without affecting the peak amplitude. The first contractures, performed at 15-20 min after the removal of diltiazem, were greatly reduced to 29 +/- 14% (4). This effect was reversed after three to five contractures in the absence of the drug. Similar results were obtained with 60 and 100 mM-K+. 4. The resting potential in control saline and after a brief exposure to 120 mM-K+ was not affected by the dihydropyridines and diltiazem. 5. Slow and fast Ca2+ currents were not modified by 1 microM-diltiazem at any stimulation rate or with pre-pulse depolarizations. Diltiazem (50 microM) did not affect the fast Ca2+ current and reduced the slow one to 48 +/- 10% (4). 7. The reduction of K+ contractures by Ca2+ channel blocking agents was not related to a blockade of Ca2+ currents. This can be tentatively explained by interactions of these compounds on membranes sites which regulate the coupling between membrane depolarization and contraction.
Gamboa-Aldeco
R
R
Department of Physiology, Biophysics and Neurosciences, Centro de Investigación y Estudios Avanzados del I.P.N., México, D.F.
Huerta
M
M
Stefani
E
E
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D011894:Rana pipiens; D013997:Time Factors
D002121:Calcium Channel Blockers; D007473:Ion Channels; D011188:Potassium; D002118:Calcium