EFFECTS OF GADOLINIUM ON LENGTH-DEPENDENT FORCE IN GUINEA-PIG PAPILLARY-MUSCLE

The degree to which stretch-activated channels operate during physiolo gical length changes in multicellular heart preparations, or how much the channels could contribute to length-dependent activation, is not k nown. We studied the relationship between muscle length and contractil e force in guinea-pig papillary muscles superfused with gadolinium chl oride (10 muM), a stretch-activated channel blocker, and compared the effects to those with nifedipine (0.25 muM), a calcium channel blocker . Gadolinium reduced contractile force statistically significantly mor e at the longer muscle lengths than at the short muscle lengths. This did not apply with nifedipine, although a marginally greater effect at longer lengths was perceptible. The results can only partly be explai ned by gadolinium having a non-specific action via the calcium channel , or Na+-Ca2+ exchange, and are consistent with the possibility that s tretch-activated channels contribute to length-dependent activation in cardiac muscle, and thus to 'Starling's Law of the Heart'.