Post-natal development of K+ currents studied in isolated rat pineal cells

• Published in: The Journal of physiology Vol. 414; no. 1; pp. 283 - 300
• Main Author: Aguayo, L G
• Format: Journal Article
• Language: English
• Published: Oxford The Physiological Society 01-07-1989; Blackwell
• Subjects: Animals; Animals, Newborn; Biological and medical sciences; Central nervous system; Electric Conductivity; Electrophysiology; Fundamental and applied biological sciences. Psychology; In Vitro Techniques; Kinetics; Pineal Gland - cytology; Pineal Gland - physiology; Potassium - physiology; Rats; Time Factors; Vertebrates: nervous system and sense organs; Endocrine gland; Rat; Rodentia; Central nervous system; Electrophysiology; Pineal body; Patch clamp method; Ionic current; Postnatal development; Vertebrata; Mammalia; Development; Potassium
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1989.sp017688

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.