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Modulation of adenosine triphosphate-sensitive potassium channel and voltage-dependent calcium channel by activin A
H Mogami1, M Kanzaki, R Nobusawa
1Department of Cell Biology, Gunma University, Maebashi, Japan.
Abstract:
The ATP-sensitive potassium channel (KATP channel) determines the membrane potential of pancreatic beta-cells and plays a critical role in the regulation of insulin secretion. The present study was conducted to investigate the effect of activin A, a member of the transforming growth factor-beta supergene family, on the KATP channel in HIT-T15 clonal hamster insulinoma cells. In an excised inside-out patch, ATP-sensitive currents with a single channel conductance of approximately 20 picosiemens were observed. In an outside-out patch, currents with identical unitary conductance were also observed. In either case, the currents were augmented by diazoxide and blocked by glibenclamide, verifying that they were KATP channel currents. When KATP channel currents were monitored in an outside-out patch, activin A added to the bath solution inhibited KATP channel currents. Upon removal of activin A, the KATP channel currents were restored, suggesting that the inhibition was not due simply to spontaneous disappearance of channel activity (run-down). The KATP channel activity was markedly reduced after the addition of activin A and was reversed by diazoxide. Besides the inhibition of KATP channel, activin A increased, in a perforated patch, the amplitude of the inward Ba2+ current in response to a depolarizing pulse from -40 to +10 mV. Under the current clamp condition, activin A induced gradual depolarization, followed by a burst of action potentials. Activin-mediated action potentials were accompanied by an elevation of the cytoplasmic free calcium concentration. These results indicate that activin A causes depolarization of the plasma membrane by inhibiting the activity of the KATP channel. In addition, activin A directly modulates the voltage-dependent calcium channel and augments calcium entry.
Insights
Activin A inhibits ATP-sensitive potassium (KATP) channels in pancreatic beta-cells, leading to membrane depolarization and increased calcium influx, crucial for insulin secretion regulation.
Area of Science:
- Cellular Electrophysiology
- Endocrinology
- Molecular Biology
Background:
- ATP-sensitive potassium (KATP) channels regulate pancreatic beta-cell membrane potential and insulin secretion.
- Activin A, a TGF-β superfamily member, has potential roles in cellular signaling.
Purpose of the Study:
- To investigate the effect of activin A on KATP channels in HIT-T15 cells.
- To elucidate the impact of activin A on pancreatic beta-cell membrane potential and calcium dynamics.
Main Methods:
- Utilized excised inside-out and outside-out patch-clamp techniques to study KATP channel activity.
- Employed perforated patch and current-clamp recordings to assess membrane potential and ion currents.
- Measured intracellular calcium concentration changes in response to activin A.
Main Results:
- Activin A inhibited KATP channel currents in a reversible manner.
- Activin A augmented inward Ba2+ currents and induced membrane depolarization.
- Activin A triggered action potentials and elevated intracellular calcium levels.
Conclusions:
- Activin A inhibits KATP channel activity, causing plasma membrane depolarization.
- Activin A modulates voltage-dependent calcium channels, enhancing calcium entry.
- These actions suggest activin A plays a role in regulating insulin secretion via beta-cell electrophysiology.