Figure 5. APD can be increased in ChR2-transduced NRVMs, using multiple blue pulses (20 ms on, 30 ms off) delivered during the repolarization phase.

(a) Action potential of control NRVMs (left black trace, without ChR2) can be elongated by 1 μM Bay K 8644 (right black trace; control reproduced as gray trace), demonstrating pharmacological APD prolongation. (b) Exemplar trace demonstrating APD lengthening by transient ChR2 activation in NRVMs. Action potentials with increasing numbers of blue pulses (i–iv, blue bars) interspersed with control APs (o). Trace shows gaps due to crosstalk compensation of the baseline shifts during blue illumination. (c) Expanded time-base display of records in (b). APD increases in a graded manner with number of blue pulses. All action potentials (control (o) and blue pulse action potentials (i–iv)) were fitted (red) to facilitate visualization after crosstalk compensation of blue-light pulses. Right bottom, comparison of fits. (d) APD with four blue pulses (iv) is significantly increased to resemble 1 μM Bay K 8644 action potential. (e) Bar graphs of average APD₈₀ for various types of action potentials, confirming a graded increase in APD with increasing blue-pulse number (mean ± sem, n = 16 channels from single coverslip). The four-blue-pulse APD₈₀ approximates pharmacologically lengthened APD₈₀ observed with 1 μM Bay K 8644 (mean ± sem, n = 82 channels). Analogous results for Bay K 8644 were obtained in a total of n = 9 coverslips. Statistical significance computed via 1-way ANOVA with Tukey-Kramer multicomparison criterion, with ** signifying p < 0.05 and * signifying p < 0.01. (f) Similar APD trends were confimed for population analysis over n = 5 coverslips (parentheses), where APD₈₀ values were normalized to values obtained from responses without a blue-light pulse. Statistical significance computed via 1-way ANOVA with Tukey-Kramer multicomparison criterion, with ** signifying p < 0.05 and * signifying p < 0.01.