MODULATION OF CA2-MUSCLE FIBERS( TRANSIENTS BY PHOTORELEASE OF CAGED NUCLEOTIDES IN FROG SKELETAL)

Action potentials and intracellular Ca2+ transients were monitored in current-clamped segments of frog skeletal muscle fibers using the trip le vaseline-gap technique. Calcium signals were measured with the fluo rescent indicator rhod 2. Action potentials produced a transient incre ase in intracellular Ca2+ that was estimated, by deconvolution of the fluorescence signals, to range between 3 and 12 mu M. The comparative effects of flash photolysis of caged adenosine 3',5'-cyclic monophosph ate (cAMP) and caged ATP on action potentials and Ca signals in muscle were investigated. The photorelease of both nucleotides produced a re duction in the amplitude of the afterpotential that follows the spike. Photorelease of cAMP and ATP prolonged the rate of decay of the Ca si gnals. No changes in either the rate of rise or in the latent period b etween stimulation and onset of the Ca signal were observed. Release o f cAMP reduced the amplitude of Ca signals, whereas release of ATP had the opposite effect. Our results show that cAMP and ATP, released abo ve their endogenous levels, modulate intracellular Ca2+ release. The c AMP modulation is more significant and may be of physiological importa nce.