Background: In neonatal heart, plasma membrane Na +-Ca 2+ exchange (NCX) and Ca 2+ channels play greater roles in intracellular Ca 2+ concentration [Ca 2+] i regulation compared with the sarcoplasmic reticulum (SR). In neonatal (aged 0-3 days) and adult (aged 84 days) rat cardiac myocytes, we determined the mechanisms underlying greater sensitivity of the neonatal myocardium to inhibition by volatile anesthetics. Methods: The effects of 1 and 2 minimum alveolar concentration halothane and sevoflurane on Ca 2+ influx during electrical stimulation in the presence or blockade of NCX and the Ca 2+ channel agonist BayK8644 were examined. [Ca 2+] i responses to caffeine were used to examine anesthetic effects on SR Ca 2+ release (via ryanodine receptor channels) and reuptake (via SR Ca 2+ adenosine triphosphatase). Ca 2+ influx via NCX was examined during rapid activation in the presence of the reversible SR Ca 2+ adenosine triphosphatase inhibitor cyclopiazonic acid and ryanodine to inhibit the SR. Efflux mode NCX was examined during activation by extracellular Na + in the absence of SR reuptake. Results: Intracellular Ca 2+ concentration transients during electrical stimulation were inhibited to a greater extent in neonates by halothane (80%) and sevoflurane (50%). Potentiation of [Ca 2+] i responses by BayK8644 (160 and 120% control in neonates and adults, respectively) was also blunted by anesthetics to a greater extent in neonates. [Ca 2+] i responses to caffeine in neonates (∼30% adult responses) were inhibited to a lesser extent compared with adults (35 vs. 60% by halothane). Both anesthetics inhibited Ca 2+ reuptake at 2 minimum alveolar concentration, again to a greater extent in adults. Reduction in NCX-mediated influx was more pronounced in neonates (90%) compared with adults (65%) but was comparable between anesthetics. Both anesthetics also reduced NCX-mediated efflux to a greater extent in neonates. Potentiation of NCX-mediated Ca 2+ efflux by extracellular Na + and NCX-mediated Ca 2+ influx by intracellular Na + were both prevented by halothane, especially in neonates. Conclusions: These data indicate that greater myocardial depression in neonates induced by volatile anesthetics may be mediated by inhibition of NCX and Ca 2+ influx channels rather than inhibition of SR Ca 2+ release.
ASJC Scopus subject areas
- Anesthesiology and Pain Medicine