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Mansim C. Okafor, Partha Mukhopadhyay, Nicholas A. Delamere; Studies on Endothelin Release and Na,K Transport in Porcine Lens. Invest. Ophthalmol. Vis. Sci. 2002;43(3):790-796.
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purpose. In an earlier study it was reported that thrombin
significantly reduces the rate of Na,K-adenosine triphosphatase
(ATPase)–mediated ion transport by porcine lens. Because thrombin
stimulates the release of endogenous endothelin (ET)-1 stores from some
tissues, and because ET-1 can cause Na,K-ATPase inhibition, this study
was designed to determine whether thrombin causes release of ET-1 from
methods. Intact porcine lenses were incubated in Krebs solution. The
concentration of ET-1 in the solution was determined by ELISA. The rate
of Na,K-ATPase-dependent ion transport was determined by measurement of
ouabain-sensitive 86Rb uptake.
results. Thrombin (1 U/mL) reduced the rate of ouabain-sensitive 86Rb uptake by approximately 40%. PD145065 (2 μM), an ET
receptor antagonist, abolished the inhibitory effect of thrombin on 86Rb uptake. Added alone, PD145065 did not alter 86Rb uptake. After an incubation period of 30 minutes,
thrombin increased the concentration of ET-1 in the bathing medium in a
dose-dependent manner. The time course of ET-1 appearance in the
bathing medium of thrombin-treated lenses showed a peak at 30 minutes
followed by a gradual decline. Consistent with the idea that release of
ET-1 from the lens is tightly regulated, neither the calcium ionophore
A23187 (1 μM) nor depolarization by potassium-rich solution caused
significant release. However, exposing the lens to insulin (150 nM)
significantly increased the appearance of ET-1 in the bathing medium.
In parallel studies, mRNA for prepro-ET-1 was detected in the
epithelium of freshly isolated lenses.
conclusions. The results of the study suggest that ET-1 is produced in porcine lens
cells and that thrombin and insulin are capable of stimulating the
release of ET-1 from the lens. Thrombin-induced inhibition of
Na,K-ATPase–dependent ion transport may be mediated in part through
the activation of ET-1 receptors by ET-1 released from the
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