Are B-type Ca2+ channels of cardiac myocytes akin to the passive ion channel in the plasma membrane Ca2+ pump?
The present study demonstrates that B-type Ca2+ channels observed in rat ventricular myocytes markedly reacted to agents known to affect the ion-motive plasma membrane Ca2+-ATPase (PMCA) pump. Chlorpromazine (CPZ)-activated B-type Ca2+ channels were completely blocked by internal application of PMCA pump inhibitors, namely La3+ (100 microm), eosin (10 microm) and AIF(3) (100 microm). Calmodulin (50 U/ml), the main endogenous positive regulator of PMCA, was unable to activate but significantly reduced CPZ-activated B-type channel activity. In the same manner, ATP (1 and 4 mm), the main energizing substrate of PMCA, was able to reversibly and significantly reduce this activity in a dose-dependent manner. Interestingly, anti-PMCA antibody 5F10, but not anti-Na/K ATPase antibody (used as a negative control) induced a marked Ba2+-conducting channel activity that shared the same characteristics with that of CPZ-activated B-type channels. 5F10-Activated channels were mostly selective towards Ba2+ , mainly had three observed conductance levels (23, 47 and 85 pS), were observed with a frequency of about 1 out of 5 membrane patches and were completely blocked by 10 microm eosin. These results suggest that B-type Ca2+ channels are some form of the PMCA pump.
Antoine
S
S
Laboratoire de Cardiologie Moléculaire et Cellulaire (CNRS ESA 8078), Hôpital Marie Lannelongue, F-92350 Le Plessis Robinson, France.
Pinet
C
C
Coulombe
A
A
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D015220:Calcium Channels / Q000145:classification* / Q000187:drug effects / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002746:Chlorpromazine / Q000494:pharmacology; D004801:Eosine Yellowish-(YS) / Q000494:pharmacology; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D000911:Antibodies, Monoclonal; D015220:Calcium Channels; D002147:Calmodulin; D001464:Barium; D007811:Lanthanum; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D004801:Eosine Yellowish-(YS); D002746:Chlorpromazine