Alterations in contractile properties and Ca2+ transients by beta‐and muscarinic receptor stimulation in ferret myocardium.

Abstract

SUMMARY1. To clarify the mechanism which regulates the time course of twitch tension when /1-and muscarinic receptors are stimulated, intracellular Ca2+ transients, Ca21 sensitivity of the contractile element and the cross-bridge cycling rate (CCR) were measured in ferret ventricular muscles. 4. In order to measure CCR, the perturbation analysis method was applied to steady-state tension of tetanic contraction. The CCR was not altered even when the tetanic tension level was decreased to 50 % by decreasing [Ca2+]0. Iso (0-1 taM) slightly decreased the tetanic tension level and increased the CCR from 2 73 to 3 25 Hz. The effect of Iso was observed when the Iso-decreased tension was recovered by an increase in [Ca2+]i. The addition of ACh (1 /tM) recovered the CCR which was increased by Iso, to the control level. Atropine (10 yM) blocked the effect of ACh, and carbachol (1 /tM) restored the CCR increased by Iso to the control level.5. The time course of Ca21 transients, Ca2+ sensitivity and CCR were antagonistically regulated by fl-and muscarinic receptor stimulation, but the time course of tension did not parallel the changes in these parameters. Therefore, these results suggest that the time course of tension, particularly the relaxation time, is not determined by the time course of Ca2+ transients, Ca2+ sensitivity and the CCR, and that other factors might be involved in the regulation of the time course of tension when /3-and muscarinic receptors are stimulated.S98 26

Mechanism of the effects of acetylcholine on the contractile properties and Ca2+ transients in ferret ventricular muscles.

“…In the IAP-treated preparations, Iso (0 1 ,UM) also increased the peaks of Ca2` (Hongo et al 1993; Fig. 1) were observed in the IAP-treated preparations (Fig.…”

“…Ferrets were anaesthetized by intraperitoneal injection of pentobarbitone (150 mg kg-') and papillary muscles were excised as previously described (Hongo et al 1993). The diameter of the preparations was 080 + 0-04 mm (mean+s.E.M., maximum = 1 15 mm, N = 27) and the length was 4-04 + 019 mm (mean + s.E.m., maximum = 7X1 mm, N = 27).…”

“…The constants for converting the light signal to [Ca2+]i were the same as those previously described (Hongo et al 1993 were calculated.…”

“…We also reported that the changes in the time course of twitch contraction do not parallel those in the time course of Ca2+ transients, Ca21 sensitivity or the cross-bridge cycling rate (CCR) when these receptors are stimulated (Hongo, Tanaka & Kurihara, 1993).…”

“…For this purpose, intracellular Ca2+ transients, Ca2+ sensitivity and CCR, the factors which regulate tension development, were measured as in the preceding paper (Hongo et al 1993). The preliminary results of this study were presented at the annual meeting of the Japanese Physiological Society and the International Society for Heart Research (Hongo, Tanaka, Suda & Hongo, Tanaka, Kiyota & Kurihara, 1990).…”