Calcium‐mobilizing and electrophysiological effects of bradykinin on cortical astrocyte subtypes in culture

Abstract

The possible consequences of activating bradykinin (Bk) receptors on identified astrocyte subtypes derived from rat cortex have been investigated in terms of: 1) mobilization of intracellular Ca2+; and 2) electrophysiological response. Bk induced a rapid, transient rise in intracellular Ca2+ in 63% of cortical type-1-like astrocytes and 44% of type-2 astrocytes tested. Experiments involving Ca(2+)-free conditions suggested that the release occurred largely from internal stores in both astrocyte subtypes. Bk receptor activation resulted in an inward current in approximately 10% of each astrocyte subtype tested using the whole-cell patch clamp technique. The use of perforated patch recording confirmed a similar population of cells responsive to Bk. The Bk-induced current was associated with a decrease in membrane conductance. The reversal potential was close to the K+ equilibrium potential, consistent with the closure of K+ channels. The current demonstrated similar EC50 values and Hill coefficients and also a marked degree of desensitization for both astrocyte subtypes. Recordings from type-1-like astrocytes indicated that the receptor mediating the electrophysiological response was of the B2 subtype. The data were consistent with the functional translation of Bk receptor occupation to physiological responses in distinct sub-populations of cortical type-1-like and type-2 astrocytes.

Two distinct inwardly rectifying conductances are expressed in long term dibutyryl‐cyclic‐AMP treated rat cultured cortical astrocytes

“…Since more than 90% of the cultured cells were GFAP ÷ A2B5 , the cultures were considered to be constituted by protoplasmic (type l-like) cortical astrocytes. This result was confirmed by electrophysiological experiments revealing that both control (n = 12) and dBcAMP treated (n = 16) astrocytes responded to the application of 100 ¢tM glutamate by displaying always inward currents with kinetics and pharmacological properties typical of the electrogenic glutamate uptake which is a distinctive feature of protoplasmic astrocytes [21].…”

Receptor-mediated calcium signalling in glial cells from mouse corpus callosum slices

“…Subpopulations of in vitro astrocytes exhibit receptors for ATP (P.,,), serotonin, glutamate, histamine, angiotensin 11, bradykinin, endothelins, somatostatin, and a-adrenergic and muscarinic agonists (Dave et al, 1991;McCarthy and Salm, 1991;Stephens et al, 1993a;McCarthy et al, 1995;Walz, 1995;Wilkin et al, 1995). With time in culture, individual astrocytes tend to lose their responsiveness to carbachol and histamine as they develop responsiveness to norepinephrine (Shao and McCarthy, 1993).…”

“…Ca+ + -sensitive fluorophores can be used to easily follow the rise of [Ca+ 'Ii after receptor activation. Thus, many neuroligand receptors have been identified in astrocytes (McDonough et al, 1988;Inagaki et al, 1991;McCarthy and Salm, 1991;Holliday and Gruol, 1993;Stephens et al, 1993a;Inagaki and Wada, 1994;Ogata et al, 1994;Salter and Hicks, 1994) and oligodendroglial cells (Kastritsis and McCarthy, 1993;He and McCarthy, 1994;Takeda et al, 1995) by their linkage to calcium signalling.…”

Neuronal Differentiation of P19 Embryonal Carcinoma Cells Modulates Kinin B2 Receptor Gene Expression and Function

“…Besides being regulated during the ontogenesis of cardiovascular and urinary systems, a large set of evidence exists showing that modulation of B2 receptor expression and function also appears during neuronal development. Thus, it has been detected in central and peripheral noradrenergic neurons, in the spinal cord, in neuronal differentiating PC12 pheochromocytoma cells, and in neuroblastoma and glia-derived cell lines (12)(13)(14)(15)(16)(17)(18). A cross-talk between the B2BKR and other hormone and neurotransmitter receptors involved in neuronal development and function has been reported, such as endothelin, serotonin, and purinergic receptors (19,20).…”