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Dihydropyridine-sensitive Ca(2+) channels in human glomerular mesangial cells
D A Hall1, P K Carmines, S C Sansom
1Department of Physiology and Biophysics, University of Nebraska Medical Center, Omaha, Nebraska 68198-4575, USA.
American Journal of Physiology. Renal Physiology
|February 8, 2000
Summary
This study confirms voltage-gated calcium channels (VGCC) in human mesangial cells. These dihydropyridine-sensitive channels regulate calcium entry crucial for agonist-induced contractions.
Area of Science:
- Cell Biology
- Physiology
- Nephrology
Background:
- Mesangial cells (MC) exhibit a biphasic intracellular calcium ([Ca2+]i) response to contractile agonists.
- The sustained phase of this response involves extracellular calcium influx, potentially mediated by voltage-gated calcium channels (VGCC).
- The presence and function of VGCC in human MC have been debated, lacking single-channel verification.
Purpose of the Study:
- To investigate the properties of the Ca2+ entry pathway responsible for sustained [Ca2+]i elevation in human MC.
- To determine if VGCC are involved in the sustained [Ca2+]i response to angiotensin II (ANG II) and high extracellular potassium ([K+]).
- To characterize the biophysical properties of these calcium channels using patch-clamp analysis.
Main Methods:
- Fura 2 fluorescence imaging to measure intracellular calcium concentrations.
- Patch-clamp electrophysiology to analyze single-channel currents.
- Application of contractile agonists (ANG II), high extracellular potassium, and dihydropyridine agonists (BAY K 8644).
- Manipulation of extracellular calcium concentrations and use of channel blockers (diltiazem).
Main Results:
- Angiotensin II (ANG II) induced sustained increases in [Ca2+]i, which were attenuated by diltiazem and dependent on external Ca2+.
- Elevated extracellular [K+] also caused a sustained rise in [Ca2+]i, similarly affected by Ca2+ removal and diltiazem.
- The dihydropyridine agonist BAY K 8644 induced sustained [Ca2+]i responses, dependent on external Ca2+.
- Patch-clamp recordings identified barium-selective channels with dihydropyridine sensitivity, exhibiting voltage-dependent gating.
Conclusions:
- Human glomerular mesangial cells possess dihydropyridine-sensitive calcium channels.
- These channels are responsible for voltage-regulated calcium entry into MC.
- This calcium influx plays a critical role in the sustained intracellular calcium increase during agonist-induced cell contraction.