Abstract
To investigate the mechanisms of receptor-mediated regulation of heart muscle contraction, we developed a tension-recording system using β-escin-skinned single cardiac cells of rats and studied the effects of agonists on myofibrillar Ca2+ sensitivity and Ca2+ release from the sarcoplasmic reticulum (SR). In pCa/tension relations, 1 µM isoproterenol plus 100 µM guanosine 5′-triphosphate (GTP) decreased the myofibrillar Ca2+ sensitivity (pCa50, the [Ca2+] required for half-maximal tension, as an indicator of the sensitivity; from 6.07 to 5.92); this effect was blocked by 1 µM metoprolol or 1 mM guanosine 5′-O-(2-thiodiphosphate) (GDPβS). Phenylephrine (10 µM) plus 100 µM GTP increased the Ca2+ sensitivity (pCa50; from 6.12 to 6.28), and this effect was blocked by 1 µM phentolamine or 1 mM GDPβS. After Ca2+ loading into the SR, 10 µM phenylephrine plus 100 µM GTP in a low-ethylene- glycol-bis(β-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA, 0.1 mM) relaxing solution induced oscillatory contractions that were attenuated by either 1 µM phentolamine or pre-treatment with 10 µM inositol 1,4,5-trisphosphate. Our results demonstrate that β1-adrenergic stimulation decreases myofibrillar Ca2+ sensitivity and that α1-adrenergic stimulation both increases the Ca2+ sensitivity and activates Ca2+ release from the agonist-sensitive SR through GTP-binding protein-related mechanisms.
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Received: 17 August 1998 / Received after revision: 23 October 1998 / Accepted: 15 December 1998
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Satoh, S., Kinugawa, S., Tsutsui, H. et al. Adrenoceptor-mediated regulation of myofibrillar Ca2+ sensitivity through the GTP-binding protein-related mechanisms: tension recording in β-escin-skinned single rat cardiac cells with preserved receptor functions. Pflügers Arch 437, 702–709 (1999). https://doi.org/10.1007/s004240050835
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DOI: https://doi.org/10.1007/s004240050835