PT - JOURNAL ARTICLE AU - TW Simon AU - CA Opdyke AU - RL Calabrese TI - Modulatory effects of FMRF-NH2 on outward currents and oscillatory activity in heart interneurons of the medicinal leech AID - 10.1523/JNEUROSCI.12-02-00525.1992 DP - 1992 Feb 01 TA - The Journal of Neuroscience PG - 525--537 VI - 12 IP - 2 4099 - http://www.jneurosci.org/content/12/2/525.short 4100 - http://www.jneurosci.org/content/12/2/525.full SO - J. Neurosci.1992 Feb 01; 12 AB - Using single-electrode voltage clamp, heart interneurons of the medicinal leech were shown to possess both a rapidly inactivating outward current, IA, and a more slowly inactivating outward current, IK. IA and IK could be separated by their voltage sensitivity and kinetic properties. FMRF-NH2 (Phe-Met-Arg-Phe-NH2) modulates IK by shifting both steady state activation and inactivation to more hyperpolarized potentials, but it does not affect the time constants. IA and IK appear to use K+ as a charge carrier; a change in the external [K+] produced a shift in the apparent reversal potential in the direction predicted with potassium as the charge carrier. Both IA and IK are sensitive to tetraethylammonium (TEA) and 4-aminopyridine (4- AP), and TEA and 4-AP both interfere with the effects of FMRF-NH2 on IK. The biophysical properties of IA and of IK in the presence and absence of FMRF-NH2 were incorporated into a Hodgkin-Huxley model of these currents that could reproduce voltage-clamp data. FMRF-NH2 produces two apparently dissimilar effects on the heartbeat rhythm-- acceleration and disruption. We suggest that both effects could result from the hyperpolarizing shifts in steady state activation and inactivation of IK.