Complex regulation of calcium current in cardiac cells. Dependence on a pertussis toxin-sensitive substrate, adenosine triphosphate, and an alpha 1-adrenoceptor.
We investigated regulation of the cardiac L-type calcium channel by intracellular ATP and by alpha 1-adrenergic agonism using single adult guinea pig ventricular cells and the whole-cell patch clamp method. Inclusion of 5 mM ATP in the patch clamp pipette prevented calcium current rundown but did not increase the maximal magnitude of the slow inward calcium current (ICa). During beta 1-adrenergic blockade with 10 microM (-)-propranolol, cells preincubated with 1 microgram/ml pertussis toxin for 2-5 h exhibited a rapid twofold increase in ICa after rupture of the membrane patch when 5 mM ATP was present in the patch clamp pipette. In the absence of ATP, the increase in ICa did not occur. In pertussis toxin-treated cells, 100 microM (-)-phenylephrine inhibited the augmentation of ICa. This inhibitory effect was blocked by 100 nM terazosin, a selective alpha 1-antagonist. The inhibitory effect of alpha 1-adrenergic agonism was not mediated by cAMP-dependent phosphodiesterase since incubation with 100 microM (-)-phenylephrine did not augment the activity of this enzyme. We conclude that regulation of the L-type calcium channel in cardiac cells is complex, and is dependent on a pertussis toxin-sensitive substrate, ATP, and an alpha 1-adrenergic receptor. The marked increase in ICa after pertussis toxin treatment in the presence of ATP indicates significant inhibition of ICa by a pertussis toxin substrate, presumably the guanine nucleotide inhibitory protein (Gi) in the basal state. The inhibitory action of (-)-phenylephrine in pertussis toxin-treated cells is consistent with modulation of ICa by an alpha 1-adrenergic receptor not coupled to Gi.
Keung
E C
EC
Department of Medicine, Veterans Administration Medical Center, San Francisco, California 94121.
Karliner
J S
JS
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D019204:GTP-Binding Proteins / Q000502:physiology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D037342:Pertussis Toxin; D010656:Phenylephrine / Q000494:pharmacology; D013379:Substrate Specificity; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D015220:Calcium Channels; D010566:Virulence Factors, Bordetella; D010656:Phenylephrine; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins