XXXX myocardium does not exhibit a slow inotropic response to stretch.

@entity1 @entity5660 @entity64
@entity1 myocardial studies reveal a biphasic increase in the force of contraction due to stretch. The first rapid response, known as the Frank-Starling response, occurs within one heartbeat of stretch. A second positive inotropic response occurs over the minutes following the initial stretch and is known as the slow force response (SFR). The SFR has been observed in @entity1 isolated whole hearts, muscle preparations and individual myocytes. We present the first direct study into the SFR in the heart of a non- @entity1 vertebrate, the @entity5660 ( @entity5660 ). We stretched ventricular trabecular muscle preparations from 88% to 98% of their optimal length and individual ventricular myocytes by 7% of their slack sarcomere length (SL). Stretch caused an immediate increase in force in both preparations, indicative of the Frank-Starling response. However, we found no significant effect of prolonged stretch on the force of contraction in either the ventricular trabecular preparations or the single myocytes. This indicates that @entity5660 ventricular myocardium does not exhibit a SFR and that, in contrast to mammals, the piscine Frank-Starling response may not be associated with the SFR. We speculate that this is due to the fish myocardium modulating cardiac output via changes in @entity64 volume to a larger extent than heart rate.
