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At least 955 records · Page 53Linked to original sources
PubMed1984

The spiracular organ of sharks and skates: anatomical evidence indicating a mechanoreceptive role.

The elasmobranch spiracular organ is a specialized receptor associated with the first visceral pouch. The structure of the sensory epithelium of the spiracular organ and the pattern of central termination of the afferent neurons that innervate it show that the spiracular organ is a mechanoreceptor closely related to the lateral line system of sense organs. Its position and orientation within the spiracular cleft suggest that it plays a role in proprioception or equilibrium-audition.

Afferent Pathways↗
PubMed1998

Differential inhibition of AE1 and AE2 anion exchangers by oxonol dyes and by novel polyaminosterol analogs of the shark antibiotic squalamine.

Oxonol and polyaminosterol drugs were examined as inhibitors of recombinant mouse AE1 and AE2 anion exchangers expressed in Xenopus laevis oocytes and were compared as inhibitors of AE1-mediated anion flux in red cells and in HL-60 cells that express AE2. The oxonols WW-781, diBA(5)C4, and diBA(3)C4 inhibited HL-60 cell Cl-/Cl- exchange with IC50 values from 1 to 7 microM, 100-1000 times less potent than their IC50 values for red cell Cl-/anion exchange. In Xenopus oocytes, diBA(5)C4 inhibited AE1-mediated Cl- efflux several hundred times more potently than that mediated by AE2. Several novel squalamine-related polyaminosterols were also evaluated as anion exchange inhibitors. In contrast to diBA(5)C4, polyaminosterol 1361 inhibited oocyte-expressed AE2 8-fold more potently than AE1 (IC50 0.6 versus 5.2 microM). The 3-fold less potent desulfo-analog, 1360, showed similar preference for AE2. It was found that 1361 also partially inhibited Cl- efflux from red cells, whereas neither polyaminosterol inhibited Cl efflux from HL60 cells. Thus, the oxonol diBA(5)C4 is >100-fold more potent as an inhibitor of AE1 than of AE2, whereas the polyaminosterols 1360 and 1361 are 8-fold more potent as inhibitors of AE2 than of AE1. Assay conditions and cell type influenced IC50 values for both classes of compounds.

Animals↗
PubMed1986

Resolution of apical from basolateral membrane of shark rectal gland.

Membrane fractions were isolated from the rectal gland of Squalus acanthias using differential centrifugation and a sucrose gradient run in the presence of 1 M KBr. Using the basolateral membrane marker Na+-K+-ATPase, we obtained a sixfold purification with the most highly purified fraction from the gradient (sp act = 336 +/- 37 mumol X mg protein-1 X h-1). Electrogenic Br- transport was used as a marker activity of the apical membrane, which enabled the identification and purification of a membrane fraction that is highly resolved from the basolateral membrane. The most active fraction was purified approximately 50-fold compared with the crude homogenate. In this fraction, the specific activity of electrogenic anion transport was 296 +/- 87 nmol X mg protein-1 X min-1, whereas the ATPase was only 17.6 +/- 5.7 mumol X mg protein-1 X h-1, representing about a 4-5% contamination of the apical fraction with the basolateral membrane.

Animals↗
PubMed1995

Evaluation of T- and L-type Ca2+ currents in shark ventricular myocytes.

Two types of Ca2+ currents with characteristics of T- and L-type Ca2+ currents were recorded in ventricular myocytes of dogfish (Squalus acanthias). The T-type Ca2+ current activated near -70 mV and had a peak current density of 9.8 pA/pF at -34 mV. The L-type Ca2+ current activated near -50 mV and had a peak current density of 10.6 pA/pF near 0 mV. The threshold for activation of the T-type Ca2+ current was 20 mV negative to that of the tetrodotoxin-sensitive Na+ current. Inactivation of the T-type Ca2+ current was rapid with a limiting time constant of 5 ms at positive potentials. The T-type Ca2+ current was not modulated by isoproterenol or acetylcholine. In dogfish the T-type Ca2+ channel has current densities equivalent to the L-type channel and is likely to activate before the Na+ channel, contributing significantly to generation of the foot of the action potential.

Amiloride↗
PubMed1983

Dual mechanism for catecholamine secretion in the dogfish shark Squalus acanthias.

Both 1,1-dimethyl-4-phenylpiperazinium iodide, a ganglionic stimulating drug (DMPP), and potassium ion (K+) cause a pressor response when injected into Squalus acanthias, an elasmobranch. The pressor responses are due to increased secretion of epinephrine and norepinephrine. The pressor response to DMPP can be blocked by prior infusion of hexamethonium, a ganglionic blocking drug. However, ganglionic blockade does not inhibit the pressor response to K+. Plasma catecholamine concentrations do not increase significantly in response to challenge with DMPP after hexamethonium infusion, but exceedingly high levels of plasma catecholamines quickly appear after K+ injection following hexamethonium infusion. It is concluded that there are at least two mechanisms controlling catecholamine secretion in the dogfish, one of which involves the ganglion cells that are intimately associated with chromaffin cells in the chromophil bodies that are so characteristic of this species and elasmobranchs in general.

Animals↗
PubMed1988

Neural control of shark rectal gland.

Veratrum alkaloids stimulated salt secretion by the isolated perfused rectal gland of Squalus acanthias. Stimulation by veratrine was prevented by the nerve channel blockers tetrodotoxin and procaine and was not evident in a preparation of dispersed rectal gland cells. Vasoactive intestinal peptide (VIP)-like immunoreactivity was detected by histological techniques in neuronal tissue within the rectal gland. Veratrine stimulation caused the release of immunoreactive VIP into the venous effluent of perfused glands. The stimulatory action of veratrine was inhibited by somatostatin, another neuropeptide known to be present in nerves of Squalus rectal gland. These findings suggest the likelihood of neural modulation of rectal gland function.

Adenosine↗
PubMed1977

Mechanism of active chloride secretion by shark rectal gland: role of Na-K-ATPase in chloride transport.

The isolated rectal gland of Squalus acanthias was stimulated to secrete chloride against an electrical and a chemical gradient when perfused in vitro by theophylline and/or dibutyryl cyclic AMP. Chloride secretion was depressed by ouabain which inhibits Na-K-ATPase. Thiocyanate and furosemide also inhibited chloride secretion but ethoxzolamide, a carbonic anhydrase inhibitor, did not. Chloride transport was highly dependent on sodium concentration in the perfusate. The intracellular concentration of chloride averaged 70-80 meq/liter in intact glands, exceeding the level expected at electrochemical equilibrium and suggesting active transport of chloride into the cell. These features suggest a tentative hypothesis for chloride secretion by the rectal gland in which the uphill transport of chloride into the cytoplasm is coupled through a membrane carrier to the downhill movement of sodium along its electrochemical gradient. The latter is maintained by the Na-K-ATPase pump while chloride is extruded into the duct by electrical forces.

Adenosine Triphosphatases↗