Abstract
Gramicidin perforated patch-clamp recordings were used to study the effects of two ς 1 receptor ligands, (+)-N-cyclopropylmethyl-N-methyl-1,4-diphenyl-1-ethyl-but-3-en-1-ylamine hydrochloride (JO 1784) and (+)-pentazocine, on the transient outward potassium current (IA) in cultured frog melanotrope cells. (+)-Pentazocine reversibly decreased the current amplitude in a dose-dependent manner. The effects of (+)-pentazocine were mimicked by JO 1784 and were markedly reduced by the ς 1 receptor antagonist,N,N-dipropyl-2-[4-methoxy-3–2(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE 100). Inactivation rate of IA was best fitted with a double exponential function, yielding time constants of 23.7 and 112.5 ms. (+)-Pentazocine (20 μM) accelerated the current decay, decreasing the time constants to 10.7 and 59 ms, respectively. Current-voltage experiments revealed that (+)-pentazocine (20 μM) did neither modify the open-state I/V curves nor the voltage dependence of IA. However, (+)-pentazocine (20 μM) shifted the steady-state inactivation curve toward more negative potentials and increased the time constant of the time-dependent removal of inactivation. In whole-cell experiments, internal dialysis of guanosine-5′-O-(3-thiophosphate) (100 μM) irreversibly prolonged the response to (+)-pentazocine. In addition, cholera toxin pretreatment (1 μg · ml−1; 12 h) suppressed the inhibition of IAby (+)-pentazocine (20 μM). It is concluded that in frog melanotrope cells, a cholera toxin-sensitive, G protein-dependent inhibition ofIA through a ς 1 receptor activation, at least partially, underlies the excitatory effect of ς ligands.
Footnotes
-
Send reprint requests to: Pr. Lionel Cazin, European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, Institut National de la Santé et de la Recherche Médicale U413, Unité Associée au Centre National de la Recherche Scientificque, University of Rouen, 76821 Mont-Saint-Aignan, France. E-mail:lionel.cazin{at}univ-rouen.fr
-
↵1 This work was supported by grants from Institut National de la Santé et de la Recherche Médicale (U 413), the Institut de Recherche Jouveinal/Parke-Davis, the European Union (Human Capital and Mobility Program; ERBCHRXCT920017), and the Conseil Régional de Haute-Normandie. O.S. was a recipient of a scholarship from the Fonds de la Recherche et de la Technologie (Conventions Industrielles de Formation par la Recherche program).
-
↵2 Current address: Institut de Recherche Jouveinal/Parke-Davis, 3–9 rue de la Loge, 94260 Fresnes, France.
-
↵3 Current address: Institut National de la Santé et de la Recherche Médicale U 488, 80, Avenue du Général Leclerc, 94276 Le Kremlin Bicêtre, France.
- Abbreviations:
- α-MSH
- α-melanocyte-stimulating hormone
- CTX
- cholera toxin
- GTPγS
- guanosine-5′-O-(3-thiophosphate)
- IA
- transient outward potassium current
- JO 1784
- (+)-N-cyclopropylmethyl-N-methyl-1,4-diphenyl-1-ethyl-but-3-en-1-ylamine hydrochloride
- NE 100
- N,N-dipropyl-2[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride
- Received September 8, 1998.
- Accepted December 2, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|