Hormones, cell volume regulation

It has been known for some time that the Cl -conductance of epithelial cells can, in addition to its regulation via cAMP, be enhanced by increases in cytosolic Ca " (cf. Fig. 3). This has been shown with Ca -ionophores [120,121] or with hormones increasing cytosolic Ca such as carbachol, neurotensin, ATP, etc. [50,103,104]. Usually these agonists have dual effects. They increase the Cl - as well as the K" -conductance [104]. Stubs et al. [122] have shown that CF cells still increase their Cl -conductance in response to ATP. Another mechanism of Cl -channel activation has been described in whole-cell patches of colonic carcinoma and RE cells [123,124] when the cells are exposed to hypotonic media they swell and increase their Cl -conductance. This is a rather general phenomenon which is present in a lot of cells [11]. In their effort to reduce cell volume in hypotonic media (regulatory... 

Polar Cell Systems for Membrane Transport Studies Direct current electrical measurement in epithelia steady-state and transient analysis, 171, 607 impedance analysis in tight epithelia, 171, 628 electrical impedance analysis of leaky epithelia theory, techniques, and leak artifact problems, 171, 642 patch-clamp experiments in epithelia activation by hormones or neurotransmitters, 171, 663 ionic permeation mechanisms in epithelia biionic potentials, dilution potentials, conductances, and streaming potentials, 171, 678 use of ionophores in epithelia characterizing membrane properties, 171, 715 cultures as epithelial models porous-bottom culture dishes for studying transport and differentiation, 171, 736 volume regulation in epithelia experimental approaches, 171, 744 scanning electrode localization of transport pathways in epithelial tissues, 171, 792. 

Although the kidneys are not considered endocrine glands per se, they are involved in hormone production. Erythropoietin is a peptide hormone that stimulates red blood cell production in bone marrow. Its primary source is the kidneys. Erythropoietin is secreted in response to renal hypoxia. Chronic renal disease may impair the secretion of erythropoietin, leading to development of anemia. The kidneys also produce enzymes. The enzyme renin is part of the renin-angiotensin-aldosterone system. As will be discussed, these substances play an important role in the regulation of plasma volume and therefore blood pressure. Other renal enzymes are needed for the conversion of vitamin D into its active form, 1,25-d i hyd ro xyv itamin D3, which is involved with calcium balance. 

The potent antidiuretic hormone AVP orchestrates the regulation of free water absorption, body fluid osmolality, cell contraction, blood volume, and blood pressure through stimulation of three G-protein-coupled receptor subtypes Vi-vascular types a and b, V2-renal, and V3-pituitary. Increased AVP secretion is the trademark of several pathophysiological disorders, including heart failure, impaired renal function, liver cirrhosis, and SIADH. As a consequence, these patients experience excess water retention or inadequate free-water excretion, which results in the dilution of sodium concentrations, frequently manifesting as clinical hyponatremia (serum sodium concentration <135mmol/L). This electrolyte imbalance increases mortality rates by 60-fold. Selective antagonism of the AVP V2 receptor promotes water... 

The antidiuretic hormone is an octapeptide released from the posterior lobe of pituitary gland. It is used in the treatment of diabetes insipidus. ADH reduces the total urine volume and absence of this hormone cause diabetes insipidus. ADH acts on collecting duct cells to increase their water permeability. It acts on V2 receptors in collecting duct and regulate their water permeability through cAMP production. 

A key determinant of the final urine concentration is antidiuretic hormone (ADH also called vasopressin). In the absence of ADH, the collecting tubule (and duct) is impermeable to water, and dilute urine is produced. However, membrane water permeability of principal cells can be increased by ADH-induced fusion of vesicles containing preformed water channels with the apical membranes (Figure 15-6). ADH secretion is regulated by serum osmolality and by volume status. 

The kidneys play an important role in maintaining a proper environment for the cells in the body. By regulating the excretion of water, salts and metabolic end products, the kidneys control the plasma osmolality (i.e., the concentration of ions in the blood), the extracellular fluid volume, and the proportions of various blood solutes. The kidneys are also involved in the production of a set of hormones that make the blood vessels (arterioles) contract in the kidneys as well as in other parts of the body. These hormones can give rise to changes in the vascular structure, and... 

---