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Post‐natal development of K+ currents studied in isolated rat pineal cells.
Author(s) -
Aguayo L G
Publication year - 1989
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.1989.sp017688
Subject(s) - pineal gland , chemistry , medicine , endocrinology , biology , biophysics , circadian rhythm
1. The voltage‐activated outward currents in diencephalon‐derived neuroendocrine pineal cells, dissociated from rats aged 1 day to 3 weeks post‐natal, were studied with the whole‐cell variation of the patch‐clamp technique and compared with those of adult rats (1‐3 months post‐natal). 2. Thirty‐five per cent of the 1‐week‐old cells displayed a single slowly inactivating outward current that had properties which distinguished it from the classical IA and IK currents. This current, named IK(d) for developmental, activated at potentials near ‐35 mV. Its time to half‐maximal activation (t 1/2) ranged from 16 ms at ‐30 mV to 4 ms at + 15 mV. No other membrane currents were apparent with depolarizing steps up to +80 mV. 3. IK(d) displayed slow inactivation at depolarized potentials. The time constant for this inactivation was on the order of several hundred milliseconds. The curve for steady‐state inactivation disclosed that the current was 50% inactivated near ‐90 mV. This current was not found in cells dissociated from animals 4 or more weeks of age. 4. The reversal potential determined from the amplitude of the tail current at various repolarizing voltages was ‐76 mV. Tetraethylammonium and 4‐aminopyridine reduced the amplitude of the current. The amplitude and time course of this current was not affected by the removal of external Ca2+. Similarly, removal of Cl‐ did not affect the current characteristics. 5. Sixty‐five per cent of the 1‐week‐old cells displayed IA and IK. IK rose slowly with time and displayed a threshold of activation near ‐20 mV. No current decay was observed during a 160 ms pulse. IA activated with step potentials positive to ‐50 mV. This current rose faster than IK(d) and IK, and it had a significant decay over a 160 ms pulse. 6. IA and IK were observed as early as 1 day after birth. Comparison of the time course of activation of IA and IK from young and adult animals showed a small increase (2‐3 ms at 0 mV) in the time to peak and half‐maximal current, respectively. With a step potential to ‐20 mV, the time constant of decay of IA increased from 34.6 ms in 2‐day‐old animals to 42.9 ms in adult animals. 7. The results indicate that unlike adult pineal cells, some cells from young animals express a kinetically distinct outward current (IK(d)) which was observed in the absence of IA and IK.(ABSTRACT TRUNCATED AT 400 WORDS)