alpha(1)-adrenergic stimulation mediates Ca(2+)-dependent inositol phosphate formation through the alpha(1B)-like adrenoceptor subtype in adult rat cardiac myocytes.
We studied the effects of increased Ca(2+) influx on alpha(1)-adrenoceptor-stimulated InsP formation in adult rat cardiac myocytes. We further examined if such effects could be mediated through a specific alpha(1)-adrenoceptor subtype. [(3)H]InsP responses to adrenaline were dependent on extracellular Ca(2+) concentration, from 0.1 microM to 2 mM, and were completely blocked by Ca(2+) removal. However, in cardiac myocytes preloaded with BAPTA, a highly selective calcium chelating agent, Ca(2+) concentrations higher than 1 microM had no effect on adrenaline-stimulated [(3)H]InsP formation. Taken together these results suggest that [(3)H]InsP formation induced by alpha(1)-adrenergic stimulation is in part mediated by increased Ca(2+) influx. Consistent with this, ionomycin, a calcium ionophore, stimulated [(3)H]InsP formation. This response was additive with the response to adrenaline stimulation implying that different signaling mechanisms may be involved. In cardiac myocytes treated with the alpha(1B)-adrenoceptor alkylating agent, CEC, [(3)H]InsP formation remained unaffected by increased Ca(2+) concentrations, a pattern similar to that observed when intracellular Ca(2+) was chelated with BAPTA. In contrast, addition of the alpha(1A)-subtype antagonist, 5'-methyl urapidil, did not affect the Ca(2+) dependence of [(3)H]InsP formation. Neither nifedipine, a voltage-dependent Ca(2+) channel blocker nor the inorganic Ca(2+) channel blockers, Ni(2+) and Co(2+), had any effect on adrenaline stimulated [(3)H]InsP, at concentrations that inhibit Ca(2+) channels. The results suggest that in adult rat cardiac myocytes, in addition to G protein-mediated response, alpha(1)-adrenergic-stimulated [(3)H]InsP formation is activated by increased Ca(2+) influx mediated by the alpha(1B)-subtype.
Seraskeris
S
S
Laboratory of Animal Physiology, Department of Zoology, School of Biology, Aristotle University of Thessaloniki, Thessaloniki 54006, Greece.
Lazou
A
A
D018674:Adrenergic Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004837:Epinephrine / Q000378:metabolism / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects; D007295:Inositol Phosphates / Q000096:biosynthesis*; D015759:Ionomycin / Q000494:pharmacology; D007502:Iron Chelating Agents / Q000494:pharmacology; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000378:metabolism*
D018674:Adrenergic Antagonists; D002121:Calcium Channel Blockers; D007295:Inositol Phosphates; D007502:Iron Chelating Agents; D018340:Receptors, Adrenergic, alpha-1; D004533:Egtazic Acid; D015759:Ionomycin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D004837:Epinephrine