Calcium and potassium changes in extracellular microenvironment of cat cerebellar cortex

Abstract

1. Local stimulus-evoked changes in concentration of extracellular calcium ions, [Ca2+]0, and potassium ions, [K+[0, were measured in the cerebellar cortex of the cat using paired ion-selected micropipettes. 2. Repetitive stimulation of 30 s duration decreased [Ca2+]0 from a base line of 1.2 mM to as low as 0.8 mM and increased [K+]0 from 3 mM to as much as 8 mM. The magnitude of the changes was directly related to stimulus frequency. Laminar analysis showed that the greatest ion changes occurred at the level of maximum parallel fiber-Purkinje cell dendrite stimulation, but that the [Ca2+]0 changes were more localized than the [K+]0 changes. 3. Combining real-time current-source density measurement with [K+]0 determination and local manganese application, showed that the Mn blocked parallel fiber-Purkinje cell synaptic transmission, but that much of the [K+]0 changes persisted. Thus, a large part of the [K+]0 flux most probably originated in the parallel fibers. In contrast, [Ca2+]0 changes were abolished by the Mn, indicating that the decrease in this ion was probably associated with synaptic transmission or dendritic events. 4. In a few cases, spreading depression occurred in the cat cerebellar cortex. This could be accompanied by decreases in [Ca2+]0 to as low as 0.12 mM and increases in [K+]0 in excess of 48 mM. 5. These results show that significant changes in [Ca2+]0 and [K+]0 occur during cerebellar stimulation and indicate possible origins of the ion fluxes in terms of neuronal elements. This work also shows that the cerebellar cortex of the cat can support spreading depression. The present results, together with those of earlier studies on [Ca2+]0 and [K+]0 changes in the presence of aminopyridine in the cat cerebellum, suggest that synaptic or dendritic electroresponsive properties may play a role in the observed [Ca2+]0 and [K+]0 changes.

In Vivo Characterization of a Smart MRI Agent That Displays an Inverse Response to Calcium Concentration

“…Unlike other Ca 2þ -responsive agents, here we see a decrease in r 1 with the increase in Ca 2þ concentration. This behavior was expected to induce an increase in MR contrast following brain activation, since extracellular Ca 2þ concentration is reduced during neuronal depolarization (27)…”

On the Role of Voltage-Dependent Calcium Channels in Calcium Signaling of AstrocytesIn Situ

“…In fact, it has been reported that pathological conditions such as ischemia or spreading depression lead to large elevations of extracellular K ϩ (60 -80 mM). These changes are accompanied by strong reductions in the concentration of extracellular C a 2ϩ (Nicholson et al, 1978). It has been suggested that the [C a 2ϩ ] i increase observed in astrocytes under these conditions is the result of C a 2ϩ influx through C a 2ϩ VOCs.…”

Cadherin Diffusion in Supported Lipid Bilayers Exhibits Calcium-Dependent Dynamic Heterogeneity

“…In cell culture, a wide range of Ca 2þ concentrations (even as low as 0.02 mM) are sometimes employed (12)(13)(14). Because cadherin structure is extremely sensitive to Ca 2þ ions, fluctuations in Ca 2þ concentration in the extracellular environment can influence the conformation of cadherin and ultimately affect their function (15)(16)(17)(18)(19)(20). While relatively small variations in Ca 2þ concentration are associated with disease pathology in vivo, more significant decreases (to~0.8 mM) were predicted in active synaptic clefts using simulations (21).…”

“…While relatively small variations in Ca 2þ concentration are associated with disease pathology in vivo, more significant decreases (to~0.8 mM) were predicted in active synaptic clefts using simulations (21). Furthermore, remarkable drops (as low as 0.3 mM) were identified experimentally in synaptic clefts during high frequency stimulation (19,20,22). At such low Ca 2þ concentrations, the binding of Ca 2þ would be significantly reduced, resulting in the loss of rigid cadherin ectodomain structure (23).…”