Electrophysiological analysis of the negative chronotropic effect of endothelin-1 in rabbit sinoatrial node cells.
1. Electrophysiological effects of endothelin-1 (ET-1) were studied in rabbit sinoatrial node (SAN) using conventional microelectrode and whole-cell voltage and current recordings. 2. In rabbit SAN, RT-PCR detected ET(A) endothelin receptor mRNA. ET-1 (100 nM) increased the cycle length of action potentials (APs) from 305 +/- 15 to 388 +/- 25 ms; this effect was antagonised by the ET(A) receptor-selective antagonist BQ-123 (1 microM). ET-1 increased AP duration (APD50) by 22%, depolarised the maximum diastolic potential (MDP) from -59 +/- 1 to -53 +/- 2 mV, shifted the take-off potential by +5 mV and decreased the pacemaker potential (PMP) slope by 15%. Under exactly the same experimental conditions, ET-1 caused a positive chronotropic effect in guinea-pig SAN with a decrease of 13% in APD50, a shift of -4 mV in the take-off potential and an increase of 8% in the PMP slope. 3. Rabbit SAN exhibited two major cell types, distinguished both by their appearances and by their electrophysiological responses to ET-1. Whereas the spontaneous pacing rate and the PMP slope were similarly decreased by ET-1 (10 nM) in both cell types, ET-1 depolarised MDP from -67 +/- 1 to -62 +/- 4 mV in spindle-shaped cells but hyperpolarised it from -73 +/- 1 to -81 +/- 3 mV in rod-shaped cells. ET-1 decreased APD50 by 8 and 52% and shifted the take-off potential by +5 and -9 mV in spindle- and rod-shaped cells, respectively. 4. ET-1 decreased the high-threshold calcium current (I(CaL)) by about 50% in both cell types, without affecting its voltage dependence, and decreased the delayed rectifier K+ current (I(K)) with significant shifts (of +4.7 and +14.0 mV in spindle- and rod-shaped cells, respectively) in its voltage dependence. It was exclusively in rod-shaped cells that ET-1 activated a sizeable amount of time-independent inward-rectifying current. 5. The hyperpolarisation-activated current (I(f)), observed exclusively in spindle-shaped cells, was significantly increased by ET-1 at membrane potentials between -74.7 and -84.7 mV whereas it was significantly decreased at more negative potentials. ET-1 significantly decreased the slope of the current-voltage (I-V) relation of the I(f) tail without changing its half-maximum voltage. 6. The overall negative chronotropic influence of ET-1 on the whole rabbit SAN is interpreted as resulting from the integration of its different actions on spindle- and rod-shaped SAN cells through electrotonic interaction.
Ono
K
K
Division of Chemical Pharmacology and Phytochemistry, National Institute of Health Sciences, 1-18-1 Kami-Yohga, Setagaya-ku, Tokyo 158-8501, Japan. kono@nihs.go.jp
Masumiya
H
H
Sakamoto
A
A
Christé
G
G
Shijuku
T
T
Tanaka
H
H
Shigenobu
K
K
Ozaki
Y
Y
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004594:Electrophysiology / Q000295:instrumentation; D019332:Endothelin-1 / Q000494:pharmacology*; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D008955:Models, Cardiovascular; D009206:Myocardium / Q000378:metabolism; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms / Q000378:metabolism; D011817:Rabbits; D017466:Receptors, Endothelin / Q000378:metabolism; D012849:Sinoatrial Node / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*
D019332:Endothelin-1; D020033:Protein Isoforms; D017466:Receptors, Endothelin