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Serotonin inhibits Ca2+ currents in porcine melanotrophs by activating 5‐HT1C and 5‐HT1A receptors.
Author(s) -
Ciranna L,
Mouginot D,
Feltz P,
Schlichter R
Publication year - 1993
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1993.sp019582
Subject(s) - depolarization , chemistry , electrophysiology , membrane potential , patch clamp , biophysics , serotonin , voltage dependent calcium channel , voltage clamp , receptor , calcium , neuroscience , biology , biochemistry , organic chemistry
1. We have investigated the effect of serotonin (5‐HT) on Ca2+ currents in cultured porcine pituitary intermediate lobe (IL) cells. Electrophysiological recordings were performed in the whole‐cell configuration of the patch‐clamp technique. All membrane currents other than Ca2+ currents were blocked pharmacologically and by ionic substitution. 2. Two types of Ca2+ currents were recorded in IL cells, differing by their activation and inactivation properties. The first type of Ca2+ current was activated at membrane potentials more positive than ‐60 mV and had a transient time course during the 100 ms depolarizing voltage steps. The properties of this current correspond to those of the T‐type or low‐voltage‐activated Ca2+ current. The second type of Ca2+ current had a threshold for activation between ‐30 and ‐20 mV and showed no sign of inactivation with time during the voltage steps. The properties of this current are similar to those of the L‐type or high‐voltage‐activated Ca2+ current. 3. Current to voltage (I‐V) relationships obtained either by conventional 100 ms voltage steps from a holding potential (VH) of ‐100 mV to various test potentials or by 800 ms voltage ramps from ‐100 to +50mV matched one another closely and showed two inward current humps corresponding to the activation of the T‐type and L‐type Ca2+ currents respectively. The ramp protocol was used to characterize the effect of 5‐HT on the Ca2+ current I‐V relationship. 4. 5‐HT (100nM to 50 microM) reversibly inhibited the amplitude of the Ca2+ current triggered by 100 ms voltage jumps from a Vh of ‐100 mV to a test potential of 0 mV. 5. The effect of 5‐HT was dose dependent with a threshold between 10 and 100 nM and a maximal effect at 10 microM. At a concentration of 10 microM, the average inhibition of Ca2+ current by 5‐HT was 18.3 +/‐ 6.5% (n = 27). 5‐HT inhibited Ba2+ current in a similar fashion. 6. When examining the effect of 5‐HT on Ca2+ current I‐V relationships, we observed a reversible inhibition of the high‐threshold component corresponding to the L‐type Ca2+ current. We never observed any effect of 5‐HT on the T‐type current. 7. The effect of 5‐HT (10 microM) was antagonized to various extents by mianserin (1 microM) but not by ketanserin (0.1 microM), suggesting the involvement of 5‐HT1C receptors.(ABSTRACT TRUNCATED AT 400 WORDS)