Abstract
The normal automaticity of rabbit SANC depends upon efficiency of the coupling between a chemical Ca2+ clock (that generates roughly periodic LCRs) and an electrical surface membrane clock (the ensemble of sarcolemmal electrogenic molecules). We have previously demonstrated tight correlations between basal state of LCR period (time from the prior AP-induced Ca2+ transient to the diastolic LCR) and AP cycle length (APCL) (interval between AP-induced Ca2+ transients) and its regulation by PKA-CAMKII dependent phosphorylation in single, isolated rabbit SANC. The role of LCRs in pacemaker activity of guinea-pig SANC or even their presence in the basal state has been recently challenged, but not systematically tested. To probe whether the guinea-pig SANC generate spontaneous diastolic LCRs and their role in the pacemaker firing, LCRs and beating rate in guinea-pig (n=8) were compared to that in rabbit SANC (n=43) at 35.5C. Rhythmically beating guinea-pig SANC do, indeed, generate spontaneous diastolic LCRs beneath sarcolemma, detected via line-scan confocal imaging (fluo-4AM,10uM) when the scanline was positioned beneath sarcolemma parallel to the long axis of the cell. Furthermore, the average LCR characteristics and the and amplitude of the LCR Ensemble Ca2+ signal, the fundamental LCR parameter that “talks to” NCX during diastole were comparable in guinea-pig and rabbit SANC (Table). Relationship between LCR period and APCL were subtended by the same linear function (R2=0.95). That LCRs in both guinea-pig and rabbit SANC contribute to the late diastolic depolarization and regulation of APCL indicate that coupled clock functions involved in pacemaker function are not species limited. Table guinea-pig rabbit LCR amplitude (F/F0)1.30±0.04∗1.43±0.03 LCR size(μm)7.36±1.20∗∗∗4.92 ±0.15 LCR duration(ms)39.78±5.836.89±1.51 LCR per cycle(Hz/100μm)6.10±1.44∗∗16.23±1.51 LCRCa2+ signal(µmxmsxΔF/F0)38.38±9.9028.30±3.42 LCR Ensemble Ca2+ signal (product of µmxmsxΔF/F0)320.24±95.63236.84±37.51 LCR period(ms)310.38±41.88315.09±12.19 APCL(ms)338.02 ±34.09378.92±9.79
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