In 24 hypertensives we evaluated, at baseline, the leukocyte filtration parameters (using the St. George’s Filtrometer), polymorphonuclear (PMN) membrane fluidity (with the fluorescent probe 1‐[4‐(trimethylamino)phenyl]‐6‐phenyl‐1,3,5‐hexatriene [TMA‐DPH]) and PMN cytosolic Ca
^{2+}
content (with the fluorescent probe Fura 2‐AM). In a subgroup of hypertensives (
n=17
) the PMN filtration parameters, PMN membrane fluidity and cytosolic Ca
^{2+}
content were evaluated after in vitro chemotactic activation (prolonged for 5 and 15 min) with two stimulating agents (4‐phorbol 12‐myristate 13‐acetate [PMA] and N‐formyl‐methionyl‐leucyl‐phenylalanine [fMLP]). It was evident, from the baseline data, that there was a significant difference in the mononuclear (MN) initial relative flow rate (IRFR), clogging rate (CR) and clogging particles (CP), and in PMN cytosolic Ca
^{2+}
content. There were, however, no differences in the filtration parameters of unfractionated leukocytes and PMNs or in PMN membrane fluidity. After activation, in normals and in hypertensives, a significant variation in PMN filtration parameters was evident. In normals no variation was present in PMN membrane fluidity or cytosolic Ca
^{2+}
content after activation. In hypertensives, however, we found an increase solely in PMN cytosolic Ca
^{2+}
content after fMLP activation. After PMN activation (at 15 min) one parameter (IRFR) of PMN filtration distinguished normal subjects from hypertensives. No difference between the two groups was found in PMN membrane fluidity or PMN cytosolic Ca
^{2+}
content after PMN activation.
