Identification and characterization of opioid and somatostatin binding sites in the opossum kidney (OK) cell line and their effect on growth

Abstract

Opioids and somatostatin analogs have been implicated in the modulation of renal water handling, but whether their action is accomplished through central and/or peripheral mechanisms remains controversial. In different cell systems, on the other hand, opioids and somatostatin inhibit cell proliferation. In the present study, we have used an established cell line, derived from opossum kidney (OK) proximal tubules, in order to characterize opioid and somatostatin receptors and to investigate the action of opioids and somatostatin on tubular epithelial tissue. Our results show the presence of one class of opioid binding sites with kappa, selectivity (KD 4.6 +/- 0.9 nM, 57,250 sites/cell), whereas delta, mu, or other subtypes of the kappa site were absent. Somatostatin presents also a high affinity site on these cells (KD 24.5 nM, 330,000 sites/cell). No effect of either opioids or somatostatin on the activity of the NA+/Pi cotransporter was observed, indicating that these agents do not affect ion transport mechanisms. However, opioid agonists and somatostatin analogs decrease OK cell proliferation in a dose-dependent manner; in the same nanomolar concentration range, they displayed reversible specific binding for these agents. The addition of diprenorphine, a general opioid antagonist, reversed the effects of opioids, with the exception of morphine. Furthermore, morphine interacts with the somatostatin receptor in this cell line too, as was the case in the breast cancer T47D cell line. Our results indicate that in the proximal tubule opioids and somatostatin do not affect transport, but they might have a role in the modulation of renal cell proliferation either during ontogenesis or in kidney repair.

Opioids and renal function

“…145 No effect of opioid agonists on the activity of the NAϩ/Pi cotransporter was observed, indicating that these agents do not affect ion transport mechanisms. 59 Opioids have been implicated in the modulation of renal water handling, but whether their action is accomplished through central or peripheral mechanisms remains controversial. Moreover, opioid receptor selectivity might result in different effects.…”

Endocytosis of the somatostatin analogue, octreotide, by the proximal tubule-derived opossum kidney (OK) cell line

“…High-affinity somatostatin binding sites have been reported in the OK cell line [31]. However, our competition studies showed that up to 100,000-fold molar excess cold octreotide only marginally inhibited the uptake of 111 In-DTPA-D-Phe 1 -octreotide.…”

Opioids modulate constitutive B-lymphocyte secretion

“…Opioids could act through a cross-interaction with other G-protein coupled sites, such as somatostatin and adrenergic receptors, as reported previously in other epithelial cell systems [60,61]. It is to note that somatostatin and beta-2-adrenergic receptors have been found in B-lymphocytes [62][63][64] triggering the same signaling pathways [65].…”