A slowly activating voltage‐dependent K+ current in rat pituitary nerve terminals.

Abstract

1. A novel slowly activating voltage-dependent K+ current was observed in isolated nerve terminals from rat neurohypophysis using the whole-cell configuration of the patch-clamp technique. 2. The activation kinetics of the slow current could be fitted assuming Hodgkin-Huxley-type kinetics, an exponential, n, of 1P3 and activation time constants decreasing from 4 s at -50 mVto 07 sat +40 mV.3. A positive shift of reversal potential was observed when [K+] was increased in the bath solution. The current is carried mainly but not exclusively by K+ ions.4. When intracellular free [Mg2+] was low (-60 /LM), average current density was 74 pA pF-1 at membrane potentials around 0 mV. In 83 % of nerve terminals current amplitude was >20 pA pF'.5. The slow current was never observed when the pipette contained 4-6 mm free Mg2+. At a physiological level of free Mg2+ (0.5 mM) the average current density was 16 pA pF1.6. When nerve terminals were analysed after patch-clamp experiments for vasopressin content by immunodetection, no difference in current amplitude was found between the terminals containing vasopressin and all analysed terminals. 7. The voltage dependence of activation was fitted by a Boltzmann equation giving a halfactivation potential of -37 mV and a slope factor of about 9 mV. 8. Tail current deactivation kinetics was biexponential with time constants of 0-12 and 1.5 s.Kinetics was dependent on the duration of the activating pulse. 9. Noise analysis of the slow current indicated a single-channel current of 0 33 pA at +6 mV, corresponding to a single-channel conductance of 4-3 pS.10. This is the first demonstration of a current similar to the slow K+ current, 'KS' in a neurone, suggesting that a protein similar to the IK,-inducing channel protein ISK (minK) may be present in peptidergic nerve terminals. 11. The activation properties are consistent with a role of the slow current in inhibition of excitability, at least at the level of the nerve terminal.

Voltage-Dependent Membrane Capacitance in Rat Pituitary Nerve Terminals Due to Gating Currents

“…Internal (pipette) solution contained (in mM) 125 Cs-glutamate, 25 CsCl, 5 NaCl, 7 MgCl 2 , 2 ATP-Na 2 , 0.1 EGTA, 0.03 cAMP, and 10 HEPES. High free [Mg 2ϩ ] (ϳ5 mM) was used to block slowly activating voltage-dependent outward currents (Kilic et al, 1996).…”

Voltage-dependent, slowly activating K + current ( I Ks ) and its augmentation by carbachol in rat pancreatic acini

“…Moreover, because of its slow deactivation, accumulation of open I Ks channels could be of pathophysiological importance at high stimulation frequencies [32]. Similar slowly activating voltage-dependent K + currents have been characterized in pituitary nerve terminals [14] and in a number of epithelial cells [11,17]. In rat colonic crypt epithelial cells, 293B-inhibitable K + channel activity was recorded in excised and cell-attached patches [33].…”

Slow Conductances Could Underlie Intrinsic Phase-Maintaining Properties of Isolated Lobster (Panulirus interruptus) Pyloric Neurons

“…A review of the literature shows multiple slow (time constants in the multiple second to minute range or current traces that take similar times to reach steady state when activated or to recover following inactivation) potassium (Adams et al, 1980; Dubois, 1981; Czternasty et al, 1989; Kumamoto and Shinnick-Gallagher, 1990; Zittlau and Walther, 1991; Sah and McLachlan, 1992; Marom and Abbott, 1994; Pedarzani and Storm, 1995; Kilic et al, 1996; Ma and Koester, 1996; Sah, 1996; Marom, 1998) (including a hyperpolarization-activated conductance qualitatively similar to our reversed potassium current) (Zittlau and Walther, 1991), sodium (Butera et al, 1999; Fleidervish and Gutnick, 1996; Fleidervish et al, 1996; Kumamoto and Shinnick-Gallagher, 1990; Marom, 1998; Toib et al, 1998),, and calcium (Adams et al, 1980; Kuo and Yang, 2001) conductances in both vertebrates and invertebrates. As such, although the precise slow conductances used here may not be present in real neurons, conductances with similar activation dynamics undoubtedly are.…”