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Related Experiment Videos

Insulin-induced hyperpolarization in retinal capillary pericytes

S Berweck1, H Thieme, A Lepple-Wienhues

  • 1Department of Clinical Physiology, Universitatsklinikum Steglitz, Freie Universität Berlin, Germany.

Investigative Ophthalmology & Visual Science
|November 1, 1993
PubMed
Summary

This study explored how insulin affects the electrical properties of retinal pericytes, which are cells that help control blood flow in the retina. Using microelectrodes, researchers found that insulin causes a small but measurable drop in membrane voltage in these cells. The effect was blocked when potassium channels were inhibited with Ba²⁺ or apamin, suggesting these channels are involved. However, blocking ATP-sensitive potassium channels or the Na⁺/K⁺ ATPase did not stop insulin's effect. High-glucose conditions did not change the results. The authors propose that insulin's effect on pericytes may help regulate blood flow in the retina, and this could be especially important in diabetes.

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Area of Science:

  • Neurophysiology of retinal microcirculation
  • Endocrinology of vascular regulation
  • Cellular mechanisms in diabetes mellitus

Background:

Current research has established that retinal pericytes influence microcirculation through contractile activity. Prior studies have shown these cells exhibit smooth muscle-like electrical properties. However, the specific mechanisms by which insulin affects pericyte membrane voltage remain unclear. No prior work had resolved whether potassium channels or other ion transporters mediate insulin's effects on pericytes. This gap motivated investigation into how insulin alters membrane voltage in these cells. The role of Ca²⁺-activated potassium channels in this process had not been tested before. Understanding these mechanisms could clarify how pericytes regulate retinal blood flow. This uncertainty drove the current study's focus on insulin's electrophysiological effects. Establishing this link could improve understanding of diabetic retinopathy pathogenesis.

Purpose Of The Study:

The aim of this research was to determine how insulin affects membrane voltage in retinal pericytes. The specific problem addressed was whether insulin-induced hyperpolarization involves potassium channels. The motivation came from the need to clarify pericyte regulation of retinal blood flow. Researchers sought to identify which ion channels mediate insulin's effects. The study focused on cultured bovine pericytes as a model system. The goal was to test whether insulin activates Ca²⁺-activated potassium channels. This approach aimed to distinguish between different potassium channel types. The findings could inform how hormonal signals influence retinal microcirculation.

Keywords:
retinal pericyte functioninsulin electrophysiologyvascular regulationmicrocirculation

Frequently Asked Questions

Insulin induces a slow hyperpolarization in retinal pericytes, with a voltage change of -3.1 mV at 10⁻⁸ mol/l.

Apamin-sensitive Ca²⁺-activated potassium channels appear to mediate insulin's effect, as apamin blocked the response.

Ba²⁺ was used to block potassium channels and determine their role in insulin-induced hyperpolarization.

Glibenclamide did not reduce insulin's hyperpolarizing effect (delta V = -2.2 mV).

High-glucose culture conditions did not significantly change resting voltage or insulin-induced hyperpolarization.

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Main Methods:

The study used conventional microelectrodes to measure membrane voltage in cultured bovine retinal pericytes. Researchers applied varying insulin concentrations to observe hyperpolarization effects. They tested the impact of Ba²⁺ to block potassium channels. Apamin was used to inhibit low-conductance Ca²⁺-activated potassium channels. Glibenclamide blocked ATP-sensitive potassium channels. Ouabain was added to suppress Na⁺/K⁺ ATPase activity. The experiments measured resting voltage and voltage changes after insulin exposure. Cultured pericytes were maintained under high-glucose conditions to assess effects on membrane properties.

Main Results:

Insulin induced a dose-dependent hyperpolarization of retinal pericyte membranes. At 10⁻⁸ mol/l, voltage change averaged -3.1 mV (n = 14). Ba²⁺ blocked insulin's effect, indicating potassium channel involvement. Apamin also abolished the hyperpolarization, suggesting Ca²⁺-activated channels. Glibenclamide did not reduce insulin's effect (delta V = -2.2 mV, n = 5). Ouabain presence did not alter insulin's hyperpolarizing action (delta V = -3.5 mV). High-glucose culture conditions did not change resting voltage or insulin response. These findings suggest apamin-sensitive channels mediate insulin's effects.

Conclusions:

The authors propose that insulin hyperpolarizes retinal pericyte membranes via Ca²⁺-activated potassium channels. Their findings suggest apamin-sensitive channels mediate this effect. They state that blocking these channels eliminates insulin's action. The study shows glibenclamide and ouabain do not affect insulin's response. High-glucose conditions did not alter membrane properties or insulin response. These results align with the hypothesis that insulin modulates pericyte contractility. The researchers suggest hormonal regulation of membrane voltage influences retinal microcirculation. They propose this mechanism may be relevant in diabetes mellitus.

The authors suggest insulin's effect may regulate pericyte contractility and retinal microcirculation, particularly in diabetes mellitus.