TY - JOUR

T1 - Regulation of lens rCx46-formed hemichannels by activation of protein kinase C, external Ca(2+) and protons

AU - Jedamzik, B

AU - Marten, I

AU - Ngezahayo, A

AU - Ernst, A

AU - Kolb, H A

PY - 2000/1/1

Y1 - 2000/1/1

N2 - Rodent lens connexin46 (rCx46) formed active voltage-dependent hemichannels when expressed in Xenopus oocytes. Time-dependent macroscopic currents were evoked upon depolarization. The observed two activation time constants were weakly voltage-dependent and in the order of hundreds of milliseconds and seconds, respectively. Occasionally, the macroscopic steady-state current and the corresponding current-voltage curve showed inactivation at high depolarizing voltages (>+50 mV). To account for the fast recovery from inactivation (<2 msec) favored by hyperpolarization, a four-state kinetic model (C(1)(closed) <--> C(2)(closed) <--> O(open) <--> I(inactivated)) is proposed. In the absence of inactivation, the macroscopic conductance decreased and inactivation became visible at voltages positive of +50 mV when the rCx46-expressing oocytes were treated with the protein-kinase-C-activators OAG or TPA, high external concentrations of Ca(2+) or H(+). However, the underlying mechanisms of OAG, H(+) or Ca(2+) action were different. While OAG did not alter the voltage-dependent activation of the rCx46-hemichannels, an increase in the external Ca(2+) or H(+) level shifted the voltage threshold for activation to more positive voltages. In contrast to Ca(2+), protons were not effective in the physiological concentration range. We propose that under physiological conditions only external Ca(2+) and intracellular PKC-dependent processes regulate rCx46 in the lens.

AB - Rodent lens connexin46 (rCx46) formed active voltage-dependent hemichannels when expressed in Xenopus oocytes. Time-dependent macroscopic currents were evoked upon depolarization. The observed two activation time constants were weakly voltage-dependent and in the order of hundreds of milliseconds and seconds, respectively. Occasionally, the macroscopic steady-state current and the corresponding current-voltage curve showed inactivation at high depolarizing voltages (>+50 mV). To account for the fast recovery from inactivation (<2 msec) favored by hyperpolarization, a four-state kinetic model (C(1)(closed) <--> C(2)(closed) <--> O(open) <--> I(inactivated)) is proposed. In the absence of inactivation, the macroscopic conductance decreased and inactivation became visible at voltages positive of +50 mV when the rCx46-expressing oocytes were treated with the protein-kinase-C-activators OAG or TPA, high external concentrations of Ca(2+) or H(+). However, the underlying mechanisms of OAG, H(+) or Ca(2+) action were different. While OAG did not alter the voltage-dependent activation of the rCx46-hemichannels, an increase in the external Ca(2+) or H(+) level shifted the voltage threshold for activation to more positive voltages. In contrast to Ca(2+), protons were not effective in the physiological concentration range. We propose that under physiological conditions only external Ca(2+) and intracellular PKC-dependent processes regulate rCx46 in the lens.

KW - Animals

KW - Calcium/metabolism

KW - Cell Membrane/drug effects

KW - Connexins/genetics

KW - Enzyme Activation

KW - Hydrogen-Ion Concentration

KW - Ion Channels/physiology

KW - Kinetics

KW - Lens, Crystalline/physiology

KW - Membrane Potentials/drug effects

KW - Oocytes/physiology

KW - Protein Kinase C/metabolism

KW - Protons

KW - Recombinant Proteins/metabolism

KW - Rodentia

KW - Tetradecanoylphorbol Acetate/pharmacology

KW - Xenopus laevis

U2 - 10.1007/s002320001005

DO - 10.1007/s002320001005

M3 - Article

C2 - 10612690

VL - 173

SP - 39

EP - 46

JO - The journal of membrane biology

JF - The journal of membrane biology

SN - 0022-2631

IS - 1

ER -