Purinergic and muscarinic receptor activation activates a common calcium entry pathway in rat neocortical neurons and glial cells.

The nature of metabotropic purinergic and muscarinic receptor-mediated increases in intracellular calcium in primary rat neocortical neurons and glial cells has been investigated using fluorescence imaging techniques. Bath-application of ATP and muscarine (10 microM) elicited a characteristic increase in intracellular calcium in both neurons and glial cells. The profile of this response consisted of an initial transient increase followed by a sustained elevation (the plateau phase) which was dependent on extracellular calcium. Examination of the pharmacological basis of the purinergic receptor-mediated calcium response using 10 microM 2-methyl-thio ATP (MeS-ATP) and UTP revealed that P(2Y) receptor activation underlies this response. The calcium influx pathway responsible for the sustained calcium response was inhibited by metal ions. In both cell types La(3+) and Zn(2+) (100 microM) effectively inhibited the plateau phase of the response, whilst 100 microM Ni(2+) had little or no effect. In conclusion, P(2Y) purinergic and muscarinic receptor activation evoke a sustained increase in intracellular calcium in neocortical neurons and glial cells. This response has similar characteristics to that we have previously described following mGlu(5) activation. We propose that in these cell types stimulation of metabotropic receptors coupled to phosphoinositide turnover activates a common calcium entry pathway that is distinct from voltage-gated calcium channels and resembles store-operated calcium entry.

Inhibition by inorganic ions of a sustained calcium signal evoked by activation of mGlu5 receptors in rat cortical neurons and glia.

The effect of mGlu receptor agonists on intracellular calcium (Ca2+) in rat cortical neurons and glial cells was studied. The responses evoked consisted of two phases; an initial transient response followed by a sustained plateau. In both cell types the order of potency of group I mGlu receptor agonists was DHPG > 1S,3R ACPD > 3-HPG. The selective mGlu5 agonist CHPG elicited responses in both cell types as did S4C3-HPG which is thought to be an mGlu5 agonist at high concentrations. S4-CPG had no effect on intracellular Ca2+ levels nor did it inhibit the action of IS,3R ACPD. These results suggest that the responses in both cell types are mediated by mGlu5 receptors. In the absence of extracellular Ca2+ ions, 1S,3R ACPD (100 microM) induced only a transient Ca2+ response which decayed to baseline with a time constant of approximately 20 s in both cell types. Subsequent readdition of Ca2+ (2 mM) to the external solution in the continued presence of 1S,3R ACPD induced a sustained Ca2+ plateau. The sustained Ca2+ plateau could be blocked by a number of inorganic cations, with an order of potency of Zn2+ > or = La3+ > Cd2+ > or = Co2+ > Ni2+ > Mg2+. Similar concentrations of Zn2+ had little effect on Ca2+-influx evoked by 25 mM K+. It is concluded that the Ca2+-entry pathway activated by mGlu5 receptors resembles store-operated Ca2+-entry pathways that have been described in other cell types.

Calcium signalling--an overview.

Calcium (Ca2+) is an almost universal intracellular messenger, controlling a diverse range of cellular processes, such as gene transcription, muscle contraction and cell proliferation. The ability of a simple ion such as Ca2+ to play a pivotal role in cell biology results from the facility that cells have to shape Ca2+ signals in the dimensions of space, time and amplitude. To generate the variety of observed Ca2+ signals, different cell types employ components selected from a Ca2+ signalling 'toolkit', which comprizes an array of signalling, homeostatic and sensory mechanisms. By mixing and matching components from the toolkit, cells can obtain Ca2+ signals that suit their physiology.