Inhibition of the calcium channel by intracellular protons in single ventricular myocytes of the guinea-pig.
1. The inhibitory effects of intracellular protons (Hi+) on the L-type Ca2+ channel activity were investigated in single ventricular myocytes of guinea-pigs by using the patch-clamp method in the open-cell-attached patch configuration, where 'run down' of the channel was partially prevented. 2. Hi+ reduced the unitary Ba2+ current of the Ca2+ channel by 10-20% without changing the maximum slope conductance. 3. Hi+ did not alter the number of channels in patches containing one or two channels. 4. Hi+ markedly reduced the mean current normalized by the unitary current, which gave the open-state probability multiplied by the number of channels in the patch. The dose-response curve between Hi+ and the open-state probability indicated half-maximum inhibition at pHi 6.6 and an apparent Hill coefficient of 1. 5. Hi+ shifted both the steady-state activation and inactivation curves in a negative direction by 10-15 mV, and the effects were reversible. 6. Hi+ did not affect the fast open-closed kinetics represented by the C-C-O scheme, apart from increasing the slow time constant of the closed time. 7. Hi+ increased the percentage of blank sweeps and reduced that of non-blank sweeps resulting in a decreased probability of channel opening. 8. Photo-oxidation with Rose Bengal abolished the reducing effect of Hi+ on the open-state probability (Po) in two out of ten experiments, suggesting the possible involvement of histidine residues in the Hi+ effect. 9. The above results indicate that Hi+ inhibits the Ba2+ current mainly by affecting the slow gating mechanism of the channel.
Kaibara
M
M
National Institute for Physiological Sciences, Okazaki, Japan.
Kameyama
M
M
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001464:Barium / Q000502:physiology; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000502:physiology*; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D011522:Protons; D012395:Rose Bengal / Q000494:pharmacology
D015220:Calcium Channels; D011522:Protons; D012395:Rose Bengal; D001464:Barium; D002118:Calcium