Osmotically Induced Conductance and Capacitance Changes in in vitro Perfused Rectal Gland Tubules of Squalus acanthias

Abstract

The rectal gland of Squalus acanthias is critically involved in the homeostasis of NaCl and water metabolism and hence in overall osmoregulation. In the present study, we have examined the acute responses of rectal gland slices and in vitro perfused rectal gland tubule (RGT) cells to the exposure to dilute and hypertonic peritubule solutions. Five series were performed. (i) With changes in osmolality, Western blots to monitor tyrosine, threonine and serine phosphorylation in rectal gland slices did not reveal clear–cut changes in phosphorylation patterns. All other series were performed in in vitro perfused RGT. (ii) Relative cell volume was estimated by fura–2 fluorescence using the emission at the isosbestic excitation wavelength of 360 nm. Hypotonic solution (–100 mmol/l NaCl) reduced fura–2 fluorescence by 16% and hypertonic solution (+100 mmol/l NaCl) had the opposite effect (+12%). (iii) Transepithelial resistance was increased markedly by hypotonic solution, probably by cell swelling, and the opposite was seen with hypertonic solutions. (iv) Whole–cell patch clamp experiments indicated that hypotonic solution hyperpolarized the cells, and increased membrane conductance and membrane capacitance. The latter two changes correlated significantly with each other. Hypertonic solution had the opposite effect. (v) Measurements of the fura–2 fluorescence ratio (340/380 nm) revealed that hypotonic solution (–NaCl) increased cytosolic Ca²⁺ activtiy ([Ca²⁺]_i). Hypertonic solution had no detectable effect on [Ca²⁺]_i. These data indicate that RGT cells are swollen by removal of NaCl from the bath solution. This causes an increase in [Ca²⁺]_i and a predominant increase in K⁺ conductance and hyperpolarization. Urea apparently permeates these cells quite well and its addition (+U) or its removal (–U) had only moderate osmotic effects. The removal of urea and replacement by mannitol produced effects similar to those seen with hypertonic NaCl solution.

Swelling-Activated Pathways in Human T-Lymphocytes Studied by Cell Volumetry and Electrorotation

“…Thus, finding f c1 is simply a matter of changing f G until the cell stop rotating (i.e., @V/@f ¼0). This was made by means of a CRF generator arranged to display f G directly (12). The CRF technique allows rapid and accurate f c1 measurements, with an acquisition time of a few seconds.…”

“…Thus, molluscian neurons reversibly increase or decrease their C C and, consequently, their surface area as they swell or shrink in hypo-or hypertonic solutions (11). In the gland cells of dogfish, hypotonicity causes a marked increase in C C , which occurs even faster than both membrane conductance increase and hyperpolarization (12). In contrast, human T-lymphocytes exhibit a slight decline in C C during moderate hypotonic swelling and Cl ÿ current induction (13).…”

Construction and function of a recombinant adenovirus encoding a human aquaporin 1-green fluorescent protein fusion product

“…This is comparable with values typically found in other epithelial cells. 29,30 When SMIE cells were exposed to a hypotonic solution (270 mOsm), swelling was observed; in addition, the C m increased slightly in control cells but markedly in infected cells (Fig 7). The difference in the extent to which C m was increased in infected cells (148 Ϯ 28%, n ϭ 4) compared with control cells (108 Ϯ 14%, n ϭ 4) was statistically significant (Figure 7, P Ͻ .05).…”