Stimulus concentration-response relations

However, the effects of Ca are not seen with all stimuli the production of Of in response to phorbol myristate acetate was unaffected in medium lacking Ca, Lanthanum, which can act as a competitive inhibitor of Ca, reduced the effect of Ca in suspensions of PMNs stimulated with FMLP , That Ca acted by entering the cell was suggested because calcium ions did not affect the binding of FMLP. However, verapamil which blocks the channel for Ca in cell membranes, produced dose-dependent inhibition of the formation of Of and of the influx of Ca. This inhibition could be overcome by increasing the concentration of Ca in the medium . The reasons for the requirement of Ca for activation by some stimuli but not by others might be related to the site at which the stimulus in question acts. PMA, for example, might act at a site beyond the point at which Ca is required. 

According to most authors the mass concentration of the airborne material is the important measure in allergic response and not the number concentration irrespective of the particle size, but Muir suggests that the intensity of the antigen stimulus to the mucosa is closely related to particle size because this determines the site of action in the respiratory tract. 

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