Abstract
The slow response of myocardial contractility to stretch has been linked to a nitric oxide mediated stretch-induced increase in ryanodine receptor Ca2+ release, revealed as an elevated diastolic Ca2+ spark rate in rat ventricular myocytes exposed to 10% stretch for 10 min (Vila Petroff et al. 2001). Here, we investigate whether stretch-induced changes in Ca2+ spark rate may occur more rapidly. Isolated rat ventricular myocytes were exposed to 10% axial stretch using computer-controlled piezo-manipulated carbon fibres, attached to the centre and one end of a cell. Controlled and reversible stretch was applied selectively to a half-cell only, allowing the non-stretched part to serve as control. Diastolic spark rate was studied using a Zeiss 510 system and software detection of signal deviation from background by > 2 S.D. Within 10 s, axial stretch transiently increased Ca2+ spark rate by 31 ± 6.5% (n = 8, p < 0.05), followed by return to background levels within 1 min. The response was not blunted by 1 mM L-NAME (nitric oxide synthase inhibitor; n = 7). We conclude that: i) axial stretch acutely raises diastolic Ca2+ spark rate in rat ventricular myocytes; ii) underlying mechanisms differ from those involved in the slow response to stretch. This study is supported by the British Heart Foundation and Eisai Co., Ltd. [J Physiol Sci. 2006;56 Suppl:S72]
