DEVELOPMENTAL DIFFERENCES IN THE REAL TIME CALCIUM TRANSIENT FOLLOWING ELECTRICAL DEPOLARIZATION IN SINGLE CARDIAC MYOCYTES

Abstract

We previously reported developmental differences in cytosolic free calcium ([Ca₁] following steady state, potassium depolarization. This study examines dynamic [Cat₁] changes-[Ca₁] transient: [Ca₁-following electrical depolarization in Immature(I)/Mature(M) single cardiac myocytes via Fura-2 fluorescence. Subanalysis of [Ca₁]_t into upstroke: (+)d[Ca₁]/dt, peak [Ca_i], and downstroke (-)d[Ca_i]/dt was performed in the presence (+) or absence (-) of Isoproterenol(ISO). Results (ANOVA) (*p<0.05 vs. M).

Peak [Ca_i] differed between groups at rest and following ISO as did (+) and (-)d[Ca_i]dt which were slower in the immature cell. Mature peak [Ca_i], (+)d[Ca_i]/dt and (-)d[Ca_i]/dt increased by 50-270% in (+)ISO while immature values decreased by up to 50%. These decreases correlated with diminished real time measures of myocyte function (% shortening) In (I) and have implications regarding the effects of inotropic agents at different stages of maturation.

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